This paper focuses on a wildlife monitoring system with wireless video transfer, which enables users to remotely monitor and control the status of cages deployed to capture wild animals. We introduce a system employing a wireless technology called diversified range IoT (DR-IoT), which is a private radio operating in the VHF band. The usage of VHF band allows us to achieve a long-range transmission, however, it also poses several challenges due to its low achievable data rates. In this paper, we investigate how to increase the capacity (number of supported cages) and realize video transfer over a low-rate wireless link with experimental results.

This paper investigates how to achieve both low-power operations of sensor nodes and accurate state estimation using Kalman filter for internet of things (IoT) monitoring employing wireless sensor networks under radio resource constraint. We consider two policies used by the base station to collect observations from the sensor nodes: (i) an oblivious policy, based on statistics of the observations, and (ii) a decentralized policy, based on autonomous decision of each sensor based on its instantaneous observation. This work introduces a wake-up receiver and wake-up signaling to both policies to improve the energy efficiency of the sensor nodes. The decentralized policy designed with random access prioritizes transmissions of instantaneous observations that are highly likely to contribute to the improvement of state estimation. Our numerical results show that the decentralized policy improves the accuracy of the estimation in comparison to the oblivious policy under the constraint on the radio resource and consumed energy when the correlation between the processes observed by the sensor nodes is low. We also clarify the degree of correlation in which the superiority of two policies changes.

This paper explores a channel selection problem for Diversified-Range IoT (DR-IoT), a wireless communication system that operates in a band with severe out-of-band emissions and has many channels with different bandwidths. Because DR-IoT operates in a band with severe out-of-band emissions, energy detection-based techniques do not work when probing to determine whether a network is operating in a given channel. Furthermore, hundreds of overlapping channels make channel scans difficult. To facilitate channel selection, DR-IoT employs an advertising channel (ACH) to exchange channel usage information among neighboring networks. If all networks can exchange their positions and current channels, they can assign channels to minimize the interference of signals sent from different networks. However, they often cannot exchange such information due to the limited ACH communication range. To mitigate this problem, we developed two new channel selection methods that leverage the ACH and received signal strength (RSS) from coordinators of other networks: minimum received beacon strength (MRBS) and closer neighbor further block (CNFB). CNFB is specifically designed to prevent networks from contending over selected channels, which coordinators cannot communicate with each other via the ACH. Our simulation results showed that communication on channels selected by CNFB achieves a 29.1 % increase in average throughput compared to a naive random selection method without ACH while outperforming the other reference methods.

Energy efficiency and information freshness are key requirements for sensor nodes serving Industrial Internet of Things (IIoT) applications, where a sink node collects informative and fresh data before a deadline, e.g., to control an external actuator. Content-based wake-up (CoWu) activates a subset of nodes that hold data relevant for the sink’s goal, thereby offering an energy-efficient way to attain objectives related to information freshness. This paper focuses on a scenario where the sink collects fresh information on top-kvalues, defined as data from the nodes observing thekhighest readings at the deadline. We introduce a new metric called top-kQuery Age of Information (k-QAoI), which allows us to characterize the performance of CoWu by considering the characteristics of the physical process. Further, we show how to select the CoWu parameters, such as its timing and threshold, to attain both information freshness and energy efficiency. The numerical results reveal the effectiveness of the CoWu approach, which is able to collect top-kdata with higher energy efficiency while reducingk-QAoI when compared to round-robin scheduling, especially when the number of nodes is large and the required size ofkis small.

The aggregation of a large amount of distributed data is one of the important functions in many IoT applications. Over–the–air computation (AirComp) realizes an efficient aggregation by exploiting the superposition property of wireless medium: all IoT nodes simultaneously transmit their signals, which are received and processed to obtain the aggregated value of their data. The conventional AirComp assumes that all nodes in a given system always join the aggregation process. However, in some practical applications, only a subset of nodes in a given system, which own updated information, are supposed to join the aggregation process. In this case, AirComp should be executed for the partial, unknown subset of nodes, which make it difficult to optimize its transmitting-receiving (Tx–Rx) parameters. To address this issue, in this paper, we propose the over– the–air computation for partial aggregation, called partial AirComp. Our numerical results show that the proposed partial AirComp achieves smaller mean–squared error (MSE) than the conventional AirComp when applied for the partial data aggregation.

An approach using a mobile sensing cluster has been proposed for search tasks such as damage assessment and rescue operations in a disaster. It dynamically forms and changes the swarms composed by multiple autonomous mobile systems that search for and capture unknown events. This mobile sensing cluster assumes that each autonomous mobile systems can acquire physical information such as radio waves emitted from the event. However, in a real environment, when autonomous mobile systems in a swarm are located far from events, they may be located in a blind zone where they cannot detect physical information emitted from the event. Therefore, a mobile sensing cluster cannot work in such blind zones. In this paper, we propose a radial spread method and an algebraic spiral method as way to search for the physical information from events in the blind zone, prior to implementing the mobile sensing cluster, and show the effectiveness of the algebraic spiral method.

An approach using a mobile sensing cluster has been proposed for search tasks such as damage assessment and rescue operations in a disaster. It dynamically forms and changes the swarms composed by multiple autonomous mobile systems that search for and capture unknown events. This mobile sensing cluster assumes that each autonomous mobile systems can acquire physical information such as radio waves emitted from the event. However, in a real environment, when autonomous mobile systems in a swarm are located far from events, they may be located in a blind zone where they cannot detect physical information emitted from the event. Therefore, a mobile sensing cluster cannot work in such blind zones. In this paper, we propose a radial spread method and an algebraic spiral method as way to search for the physical information from events in the blind zone, prior to implementing the mobile sensing cluster, and show the effectiveness of the algebraic spiral method.

This paper focuses on top–k query in cluster–based wireless sensor networks (WSNs) employing wake–up receivers, which aims to grasp the information on top–k data efficiently in terms of energy consumed by sensor nodes. As a wake–up control for top–k query, countdown content–based wake–up (CDCoWu) has been proposed. CDCoWU selectively activates sensor nodes storing data belonging to top–k dataset, and its superiority to a conventional identity–based wake–up (IDWu) has been confirmed for a single–hop network accommodating a large number of nodes. In this paper, we extend these wake–up control to a cluster–based WSN, a common network structure of WSN. The cluster–based WSN contains nodes called cluster heads that relay wake–up signals and data for their cluster members. The proposed cluster–based wake–up control conducts activations and data collections of different clusters sequentially while the results of data collections at a cluster are exploited for reducing unnecessary data transmissions at the other clusters. We also introduce a hybrid mechanism of wake–up control, where a wake–up control employed at each cluster is selected between CDCoWu and IDWu according to its number of cluster members. Our simulation results show that the proposed hybrid wake–up control achieves smaller energy consumption and data collection delay than the control solely employing CDCoWu or IDWu.

In real environments, it is difficult to predict the occurrence of events such as damage to structures and people in need of rescue, and the location and number of most such events are unknown. We have proposed a Mobile Sensing Cluster (MSC) to search for and capture unknown events. MSC dynamically forms multiple swarms of autonomous mobile systems such as robots and UAVs based on swarm intelligence, and it achieves search and capture of more unknown events in a short time. However, the effectiveness of MSC strongly depends on the number of autonomous mobile systems used. In this paper, we propose a Self-Cloning Mobile Sensing Cluster to achieve the search and capture of unknown events beyond the actual number of autonomous mobile systems, and we discuss its basic effectiveness based on an evaluation using simulations. The Self-Cloning MSC consists of both actual mobile systems in physical space and virtual cloned mobile entities in cyber space. This virtually increases the number of autonomous mobile systems with the cloned mobile entities, allowing them to form diverse swarms based on MSC.

Stable and low-latency wireless communications are essential for the digital transformation in various industries. Multi-Diversity WLAN (MD-WLAN) incorporating three different types of diversities provides stable low-latency communications suitable for usages in many industries. In this demonstration, we explain the concept, design, and prototype of MD-WLAN, and then demonstrate the low-latency live video streaming over MD-WLAN using the prototype system. We confirm that multi-radio, multi-receiver, and FEC control of MD-WLAN contribute to the significant improvement of robustness and stability of low-latency video streaming.

In this paper, we focus on anomaly detection in on–demand wireless sensor networks (WSNs), where a wake–up receiver operating with ultra–low power consumption is applied to each sensor node. In order to achieve high accuracy for anomaly detection while reducing power consumption, we need to selectively collect sensing data contributing to the improvement of detection accuracy. To this end, we exploit content–based wake– up (CoWu), where sensor nodes can be selectively woken up based on their observations and the condition set by a data collection node. We propose anomaly region based wake–up (ARWu) that estimates the region of the normal/anomaly data and selectively wakes up nodes that are expected to store anomaly data by employing CoWu. With computer simulations, we show that the proposed wake–up control achieves smaller energy consumption and delay to satisfy a given accuracy of anomaly detection than the conventional wake–up control.

This paper aims to improve the efficiency of wake-up control for top-$k$query in wireless sensor networks (WSNs) by introducing a function to estimate the data distribution of sensors. In order to minimize the wasteful wake-up of nodes outside the top-$k$set, the sink gradually enlarges the search region of data from the highest value by employing countdown content-based wake-up (CDCoWu). In this case, the step size to enlarge the search region plays an important role: a larger step causes many nodes to simultaneously wake up, which leads to severe congestion, while a smaller step leads to the failed wake-up trial with no replies. In this paper, in order for the sink to appropriately select the step size, we introduce kernel density estimation into wake-up control, by which the sink first estimates the probability density function (PDF) of data owned by sensor nodes. The efficiency of CDCoWu can be improved with more accurate estimation on PDF, which, however, requires larger estimation cost. In this paper, we analyze the trade off between the accuracy of estimation and efficiency of CDCoWu, and investigate whether the overall efficiency in terms of energy consumption and delay can be improved by the proposed wake-up control with density estimation. Our numerical results show that the proposed wake-up control achieves better energy effi-ciency and data collection delay than the conventional CDCoWu employing a fixed step size.

Stable wireless connections are required for realtime applications employing high data rate video streaming. Each of Multi-AP system and Multi-Link aggregation is effective to make WLAN connections stable, and we propose a combined Multi-AP Multi-Link system for realizing more stability in the practical use. In our proposed system, APs, which have different types of transmission queues, transmit a stream collaboratively with the support of a coordinator. In the demonstration, we will show that the proposed system realizes high quality video streaming even when WLAN links suffer from interference caused by surrounding devices.

In this paper, we advocate utilizing link-level broadcast of wireless LAN (WLAN) for real-time data transmissions from a drone to ground access points (APs) in order to enhance their robustness and spectral efficiency. A WLAN station (STA) is installed on a drone, which broadcasts its real-time data to surrounding multi-APs deployed over a ground field. In order to enhance the reliability of data transmissions, we also apply packet-level forward error correction (FEC). We conduct a field trial with our experimental testbed where all the above functions are implemented into the off-the-shelf WLAN equipment. Our experimental results show that multi-AP broadcast transmissions with packet-level FEC achieve better packet delivery ratio with smaller channel occupancy period than a common approach utilizing unicast transmissions.

Stable wireless connections are required for ITS applications employing real-time video streaming. It is effective to enable multiple links which work on different channels in order to make WLAN connections stable. Therefore, we propose a transmission control scheme for multi-link WLAN assuming the real-time video streaming. In our proposed scheme, radio units, which have different types of transmission queues, transmit a video streaming collaboratively with the minimum support of a coordinator. A multi-radio receiver controls A-MPDU transmissions of the radio units using Block-Acks including a shared scoreboard context to avoid duplicated retransmissions. Our simulation results show that the proposed scheme reduces both average latency and maximum latency of video streaming traffic significantly when wireless link conditions change dynamically.

To collect vital data from a group of outdoor exercisers in real-time and reliably, we propose a wireless multihop network system based on a flooding/time division multiple access (TDMA) protocol with an extended superframe structure. For wireless vital sensor nodes (VSNs) put to the bodies of exercisers, the system first randomly and temporarily divides a whole group of VSNs into several subgroups and assigns a distinct superframe to each subgroup. Then, when VSNs move around in a ground, the system adaptively changes subgroup members so as to make them uniformly and widely spread in the ground by using the location information on all the VSNs.In this paper, we evaluate the performance of the system by an experiment. We conduct the experiment in an outdoor ground of 60m×90m for 45 min, involving 50 subjects, where we put VSNs to 18 subjects out of them. We show in the performance evaluation that the system can collect vital data from the 18 subjects even when all the subjects perform a variety of exercises, once in 2 sec in average, for 45 min regularly, and in 94.9 % data collection rate reliably.

In this paper, we advocate applying the concept of wake-up radio to distributed estimation in wireless sensor networks. With distributed estimation, where sensing data of multiple nodes are used for estimating a target observation, the energy consumption can be reduced by making only a subset of nodes in the network transmit their data, such that the collected data can guarantee the required estimation accuracy. In this case, a sink needs to selectively wake up sensor nodes whose data can contribute to the improvement of estimation accuracy. In this paper, we propose a wake-up signaling called estimative sampling (ES) that can realize the selective wake-up of desired nodes. The ES method includes a mechanism that dynamically searches the desired nodes over a distribution of sensing data. With numerical results obtained by computer simulations, we show that the distributed estimation with ES method achieves lower energy consumption than that with conventional identity-based wake-up while satisfying the required accuracy.

This paper considers the periodical top-k query for wireless sensors, where a sink periodically seeks top-k values and corresponding nodes-IDs in a sensing field. We advocate applying wake-up receivers in this scenario in order to reduce the wasteful energy consumption of sensor nodes. A wake-up control is proposed for the sink to collect top-k data with temporal correlation with small amount of energy. Specifically, the proposed scheme employs different types of wake-up control, which aims to wake up only the subset of nodes whose owning data contribute to the identification of current top-k set by exploiting temporal correlation. The numerical results confirm the effectiveness of our proposed scheme compared with the conventional wake-up control for top-k query in terms of average energy consumption, especially when the degree of correlation is high.

In mobile sensing where autonomous mobile robots equipped with diverse types of sensors perform sensing operations over a sensing field, the number and positions of sensing targets can be unknown, therefore, robots need to search for sensing targets by themselves. In order to realize an efficient search with a group of robots, this paper introduces an algorithm called mobile sensing cluster, where robots form a swarm with data exchange through wireless communications. We focus on a scenario where mobile sensing cluster is applied to search for multiple targets emitting indistinguishable signals, e.g., search for gas sources. In this case, it becomes difficult for mobile robots to decide appropriate directions to move toward individual targets. In this paper, we propose algorithms for mobile robots to efficiently search for these indistinguishable multiple targets, and investigate their search efficiency by computer simulations.

This paper proposes content-based control of wakeup receivers for data collection in wireless sensor networks. The wake-up procedure is designed with a goal of waking up only the subset of the sensor nodes which have the relevant data observations. This prevents the sensors with less relevant data from waking up and wasting energy, which is inevitable when employing conventional ID-based wake-up control. We apply the proposed content-based wake-up scheme to top- k query, where the sink attempts to collect information on the set of nodes that own top- k observations from the sensing field. Assuming medium access based on p-persistent CSMA, we design a content-based wake-up control scheme suited for the data collection of top- k query. We analyze the scheme theoretically in terms of data collection delay and energy-efficiency and compare it to the ID-based wake-up. The numerical results confirm the effectiveness of the proposed content-based wake-up control, especially when the number of sensor nodes is large.

Reliable and real-time vital signs monitoring is essential to promote health and prevent disease/injury for a group of exercisers spread in a sports ground such as schoolchildren and professional athletes. For that purpose, we developed a wireless vital signs collection system and confirmed it worked effectively, but unfortunately, it required an infrastructure of data forwarding nodes placed around the area of interest. We really wanted to realize it infrastructurelessly.Now, we are developing an infrastructureless multi-hop wireless network system which has the same vital sensing and wireless communication functions, and we have so far successfully conducted one indoor experiment and two outdoor experiments for footballer subjects. In this paper, we will outline the design concept and show the experimental results.

This paper focuses on on-demand wireless sensor networks (WSNs) where a main radio interface (IF) used for data communications by each node is remotely activated through its secondary radio called wake-up receiver. The energy-efficiency achieved by on-demand WSNs highly depends on the trade-off between the wake-up range (i.e., the range within which a wake-up signaling is possible) and power consumption of wake-up receiver. With larger (smaller) wake-up range, the required number of hops for data delivery can be smaller (larger) while larger (smaller) power consumption of wake-up receiver is required to achieve higher (lower) receiver sensitivity. In this paper, we analyze the impact of this trade-off on the overall energy-efficiency of on-demand WSNs. Furthermore, we propose a multi-hop wake-up control with small control overhead, which is achieved by making intermediate nodes jointly send several control messages for wake-up operations with a single transmission. Our simulation results reveal the inherent trade-off between sensitivity and power consumption of wake-up receiver, and also show that the proposed multi-hop wake-up control significantly improves the energy-efficiency of on-demand WSNs.

The authors try to construct a novel sensor networking scheme that obtains the location of sensor nodes using image processing in order to enable dynamic routing when the speed and the density of the sensor nodes become high. In this scheme, visual object detection is applied for the localization of sensor nodes; however, certain failures occur during the region merging process, which is required for schemes based on sliding windows. For the widely used pairwise max suppression(PMS), the most significant problem is the fixed threshold for region merging. To solve this problem, this paper proposes a novel scheme for region merging that adopts adaptive thresholding for the existing PMS. The threshold is appropriately determined by taking into account the total number of detection targets. The experimental results, conducted using a dataset composed of top-view images generated from a CG-based virtual space, showed that the miss rate can be reduced to approximately 67.4% of the existing PMS.

This paper focuses on on-demand wireless sensor networks (WSNs) where a wake-up receiver is installed into each node. In on-demand WSNs, each node sends a wake-up signal including a wake-up ID assigned to a specific destination node in order to remotely activate its main radio interface. This wake-up control helps each node to reduce energy consumed during idle periods, however, the wake-up signal transmitted before every data transmission results in overhead causing degradation of communication quality and increase of energy consumption at each sender node. In order to reduce the overhead for wake-up control, a scheme called Double Modulation (DM) has been proposed, where each node embeds a sensing data to be transmitted into the payload field of a wake-up signal. However, the efficiency of DM scheme becomes smaller as the size of sensing data is increased. Therefore, in this paper, we propose a scheme called Overhearing (OH) that can alleviate the negative impact of wake-up overhead for any size of sensing data. In OH scheme, each node observes frames transmitted by a destination node and suppresses the transmission of wake-up signal when detecting the active state of their destination. Furthermore, we propose a hybrid scheme that combines OH and DM schemes. Our simulation results show that the proposed hybrid scheme can effectively reduce the negative impact of wake-up overhead.

CSMA is the de facto standard in wireless LANs (WLANs), where one transceiver is used for both the control and data planes. When many nodes contend to access a same channel, the WLAN transceiver performs carrier sense during most time, which wastes much energy. Dynamic adjustment of parameters (contention window) is suggested in previous works for improving network throughput, but this is also realized at the cost of continuously monitoring the channel with large power consumption. To solve these problems, in this paper, we suggest tightly integrating a lower power wake-up radio (WuR) with the power-hungry WLAN module. Specifically, (i) The WuR is used to monitor the channel and conduct carrier sense. It activates the WLAN module for actual transmissions when the channel gets ready. (ii) The WuR is used to measure the inter-frame space, based on which contention window is adjusted accordingly. Extensive simulation evaluations confirm that the proposed scheme (WuR-CSMA) effectively reduces the duty ratio of WLAN modules and improves system throughput, achieving both energy and spectral efficiency compared with the conventional schemes.

Wireless sensor and actuator networks (WSANs) are required to achieve both energy-efficiency and low-latency in order to prolong the network lifetime while being able to quickly respond to intermittently-transmitted control commands. These two requirements are in general in a relationship of trade-off when each node operates with well-known duty-cycling modes: nodes need to make their radio interfaces (IFs) frequently active in order to promptly detect the communication requests from the other nodes. One approach to break this inherent trade-off, which has been actively studied in recent literature, is the introduction of wake-up receiver that is installed into each node and used only for detecting the communication requests. The radio IF in each node is woken up only when needed through a wake-up message received by the wake-up receiver. While the effectiveness of this type of on-demand WSANs has been shown in several studies by theoretical analysis and computer simulations, its implementation and large-scale experimental investigations are missing. Therefore, in this paper, we first design and implement radio-on-demand sensor and actuator networks (ROD-SAN) including all protocols to realize on-demand WSANs, from the lowest layer of wake-up signaling to the application layer offering the functionalities of information monitoring and networked control. Then, we show experimental results obtained through our field trial in which 20 nodes are deployed in an outdoor area with the scale of 450m X 200m. The numerical results provide us with practical insights on the effectiveness as well as limitations of on-demand WSANs.

In this paper, we attempt to improve the efficiency of random access employed for a massive number of energy-constrained M2M devices to transmit their data to a base station (BS) by exploiting relaying and interference cancellation (IC). Each device transmits a single packet with a minimum required power, which is then forwarded by surrounding relay(s) to derive a benefit of IC at BS. While IC can increase the number of packets successfully decoded at BS, relaying increases the overall traffic load since each relay joins the random access sharing the radio resource with the devices in order to forward the received packets. Taking this trade-off into account, we investigate a possible gain brought by relaying and IC in terms of average number of successfully received packets at BS. Our numerical results show that the efficiency of random access from a massive number of devices can be significantly improved only by uniformly deploying a small number of relays inside a cell. The proposed approach does not require each M2M device to redundantly transmit their data to apply IC, which is favorable from a viewpoint of energy-efficiency of each battery-operated M2M device.

Energy harvesting wireless sensor network (EHWSNs) are being actively studied in order to solve the problems faced by battery-operated WSNs, namely the cost for battery replacement and impacts on the environment. In EH-WSNs, each node harvests ambient energy, such as light, heat, vibration, and uses it for sensing, computations, and wireless communications, where the amount of harvested energy of each node varies depending on their surrounding environments. MAC protocols for EH-WSNs need to be designed to achieve high throughput and fairness, however, the conventional MAC protocols proposed for EH-WSNs do not adapt to the harvesting rate of each node, resulting in poor fairness. In this paper, we propose a fair MAC protocol based on polling scheme for EH-WSNs. The proposed scheme adjusts contention probability of each node according to the individual harvesting rate, thereby increasing throughput achieved by nodes with low harvesting rate. We evaluate throughput and fairness of the proposed fair polling scheme by computer simulations, and show that the proposed scheme can improve fairness with little degradation of the overall network throughput.

Sensor networks are playing more and more important roles, e.g., accurately monitoring the generation and consumption of electric power for the purpose of smart grid. In these applications, sensor nodes, working with battery, should be put into sleep in the idle state to prolong network lifetime and be activated on demand to ensure real-time response. State-of-the-art schemes merely exploiting duty-cycling cannot simultaneously satisfy these two requirements. In this paper, we exploit frame length of 802.15.4g signals for the wake-up control of sensor nodes. A wake-up ID is modulated onto frame lengths of consecutive signals defined by the mode switch mechanism, transmitted by a sensor node using the standard 802.15.4g protocol, and detected by a non-802.15.4g, low-power wake-up receiver. A prototype wake-up receiver is implemented by using FPGA. It consists of two-stage wake-up control in the sense that duty-cycling is also exploited in the detection of wake-up signals. The proposed scheme achieves a better tradeoff between power-consumption and wake-up latency, compared with the conventional duty-cycling schemes. The experimental evaluation confirms that the wake-up control meets the sensitivity requirement of data communications.

In order to reduce energy wastefully consumed by WiFi device, Radio-On-Demand Networks (ROD) has been proposed, which offers wireless access in an on-demand manner. Each WiFi device in ROD is equipped with a low-power wake-up receiver which is capable of detecting the length of frames observed over WiFi channels through envelope detection and on-off-keying (OOK) processing. Once the wake-up receiver detects the predefined set of length of WiFi frames included in the wake-up signal transmitted by the other WiFi device, it turns its main WiFi module on. The wake-up receiver extracts WiFi signals over all WiFi channels at 2.4 GHz band. On the other hand, a WiFi device, which tries to wake up the other device, selects a wake-up channel, a channel to transmit its wake-up signal. In this case, the receiver observes an envelope which is the combination of the wake-up signal and the interfering signals existing over all WiFi channels. Here, how to select the wake-up channel is a key issue when the degree of interference is different among multiple WiFi channels. In this paper, with different degree of interference in each channel, we evaluate the impact of wake-up channel selection on the wake-up success probability of WiFi device. Besides simulations results, we also present experimental results which are obtained with our developed prototype of wake-up receiver.

In order to reduce energy wastefully consumed by access points (APs) in wireless LAN (WLAN), Radio-On-Demand (ROD) WLAN has been proposed, which offers wireless access only when and where it is needed in an on-demand manner. Each AP in ROD is equipped with a wake-up receiver, which transits a state of AP from sleep to active by receiving a wake-up signal from a station (STA). However, if there are several APs having the same wake-up ID around a STA, a wake-up request from STA causes more than one AP to wake up though STA only needs a single AP. In this paper, in order to reduce the number of APs redundantly woken up in such a situation, we propose a probability-based wake-up mechanism. With the proposed mechanism, each AP does not always wake up after receiving the wake-up request. Instead, each AP decides whether it should wake up or not based on the wake-up probability. This probability is adjusted in such a way that only APs suited for serving the corresponding STA have the higher probability to wake up while the other APs maintain a lower probability. By computer simulations, we show that our proposed mechanism can significantly reduce the number of redundant wake-up while keeping the adverse impact on their usability and quality of service (QoS) small.

This paper investigates the impact of hidden nodes on wake-up signaling employed to realize energy-efficient wireless LAN (WLAN). The considered wake-up mechanism is based on frame length modulation which exploits WLAN frames as a wake-up signal: a station with communications demands transmits a series of WLAN frames with length corresponding to wake-up ID of the target receiver in a sleep mode. The wake-up receiver attached to the target of wake-up signal only performs a limited signal processing to detect each frame length, which consumes little amount of energy. Since WLAN frames are transmitted with carrier sense multiple access (CSMA) protocol, the wake-up signaling with frame length modulation is vulnerable to hidden node problem. In this paper, we theoretically investigate the impact of hidden nodes on the frame length detection. We also evaluate the wake-up failure probability when the length of frame transmitted by hidden nodes is decided according to a practical trace data of WLAN frames. Our analysis and obtained results give us the insight on how to alleviate the negative impact of hidden nodes on wake-up signaling.

In this paper, we design a simple, low-cost, and low-power wake-up receiver which can be used for an IEEE 802.11-compliant device to remotely wake up the other devices by utilizing its own wireless LAN (WLAN) signals. A typical usage scenario of such a wake-up receiver is energy management of WiFi device: a device equipped with the wake-up receiver turns WiFi interface off when there is no communication demand, which is powered-on only when the wake-up receiver detects a wake-up signal transmitted by the other WiFi device. The employed wake-up mechanism utilizes the length of 802.11 data frame generated by a WiFi transmitter to differentiate the information conveyed to the wake-up receiver. The wake-up receiver is designed to reliably detect the length of transmitted data frame only with simple envelope detection and limited signal processing. We develop a prototype of the wake-up receiver and investigate the detection performance of the envelope of 802.11 signals. Based on the obtained experimental results, we select appropriate parameters employed by the wake-up receiver to improve the detection performance. Our numerical results show that the proposed wake-up receiver achieves much larger detection range than the off-the-shelf, commercial receiver having the similar functionality.

Recent investigations show that (i) access points (APs) of wireless local area networks (WLANs) are idle during much of the time, and, (ii) an AP in its idle state without forwarding any packets still consumes a large percentage of power. Therefore, it is necessary to put idle APs into sleep so as to realize green WLANs. The problem, however, is how to quickly and reliably activate APs from sleep when nodes initiate new data flows. Aiming at realizing Radio-On-Demand WLANs, in this paper, we suggest exploiting burst transmission of WLAN frames to convey wake-up IDs from nodes to APs. Our contribution is two-fold: (i) The burst transmission prevents interfering WLAN signals from breaking in, and, (ii) We re-interpret the sequence of WLAN frames for wake-up signaling as an equivalent ID. Based on the analysis of hamming distance among equivalent IDs, we further suggest using partial correlation to reduce the error rate of wake-up signals. The effectiveness of the proposed scheme is confirmed by both theoretical analysis and simulation evaluations.

This paper investigates wake-up ID and protocol design for radio-on-demand (ROD) wireless LAN (WLAN) where wake-up radio is applied to access point (AP) in order to save energy consumed by WLAN. Each AP in ROD WLAN is transited to a sleep state when there is no associated user. A wake-up receiver installed into each AP is used to detect a wake-up signal transmitted by a station (STA) upon communications demands. Each STA specifies an AP to wake up by embedding ID of the target AP into the wake-up signal. In this paper, we propose a wake-up ID assignment and ID matching which can reduce the probability of false wake-up caused by bit errors over wireless channels. The proposed scheme generates wake-up ID of each AP based on ESSID in such a way that certain number of hamming distances is maintained among different wake-up IDs. The AP wakes up when the hamming distance between the received ID, possibly containing bit errors, and its assigned ID is less than a predetermined value. The numerical results obtained by theoretical analysis and computer simulation show that the proposed scheme can effectively reduce the false wake-up probabilities with short ID length and very simple operations at wake-up receivers. We also propose a wake-up protocol for ROD WLAN to reduce energy wastefully consumed by APs which are redundantly woken up with the proposed ID assignment/matching. Our simulation results show that ROD WLAN with the proposed protocol achieves much better energy-efficiency than ROD WLAN without the proposed protocol and WLAN without applying ROD technologies.

Access points (APs) of wireless LANs (WLANs), always powered on and ready to serve mobile nodes, consume a large amount of power in total, but are idle during much of the time. Previous protocol-based sleep-wakeup scheduling schemes partially solve this problem, but the large wakeup delay remains a problem. Aiming at realizing Radio-On-Demand WLANs, in this paper, we suggest using an additional wakeup transceiver to convey wakeup signals from nodes to APs. APs in the sleep mode are activated by nodes when new data flows are initiated, where the wakeup delay is very low. The proposed wakeup transceiver works on the 2.4GHz ISM band and shares antenna with a co-located WLAN module to reduce hardware cost. The wakeup receiver is designed to be simple but very reliable, and consume a very low power. The contribution of this paper is two-fold: (i) Wakeup signals are designed to co-exist with WLAN signals by exploiting the carrier sense mechanism of WLAN devices, and, (ii), explicit signal recognition is used to achieve an extremely low false wakeup probability in an environment where the number of WLAN signals is overwhelming. Testbed experiments confirm that the proposed scheme, besides its simplicity, has good performance in both frame error rate and false wakeup probability.

In this paper, we introduce Radio-On-Demand (ROD) wireless LAN (WLAN) in which access points (APs) are put into a sleep mode during idle periods and woken up by stations (STAs) upon communications demands. The on-demand wake-up is realized by a wake-up receiver which is equipped with each AP and is used to detect a wake-up signal transmitted by STA. In this paper, in order to reduce the hardware installation cost at STA, we advocate to utilize wireless LAN frames transmitted by each STA as a wake-up signal to awake the target AP. The STA generates a wake-up signal by devising WLAN signal: each STA creates a series of WLAN frames with different length to which the information on wake-up ID is embedded. The wake-up receiver extracts the wake-up ID from the received frames with a simple detector which ensures its low-power operation. We evaluate false negative (STA fails to wake up the target AP) and false positive (AP falsely wakes up without an intended wake-up signal) probabilities of our proposed on-demand wake-up scheme with computer simulations. The numerical results show that the proposed scheme achieves the false negative probability of about 10-2when the detection error ratio of `1' is less than 10-3. We also show that the false positive probability can be largely reduced by employing long WLAN frames to generate each wake-up signal. These results confirm that the proposed wake-up scheme is a promising approach to reducing wasteful energy consumed by idle APs in WLAN.

Optimized resource allocation of the Downlink (DL) in wireless systems utilizing Multi-Carrier (MC) transmission requires Channel State Information (CSI) feedback for each user/subchannel to the Base Station (BS), consuming a high amount of Uplink (UL) radio resources. To alleviate this problem, several works have considered contention-based CSI feedback in the UL control channel. We propose such a feedback scheme for a generic MC system, based on the idea of variable collision protection, where the probability that a feedback information experiences a collision depends on its importance. By partitioning the CSI into orthogonal layers of priority, and allocating different numbers of feedback slots to each layer, this scheme ensures that the feedback success probability is higher for the CSI with better quality, which is more likely to be used by the scheduler. Furthermore, we present a theoretical performance analysis of the proposed scheme, assuming Maximum CSI (Max CSI) and normalized Proportional Fair Scheduler (PFS), where a tight approximation of the achievable throughput is obtained assuming discrete Adaptive Modulation (AM) and CSI feedback which are relevant for the practical systems. Analytical and simulation results show that our proposed scheme provides an excellent trade-off between system performance and feedback overhead.

This paper considers secondary usage of spectrum resources that are allocated to frequency division duplexing (FDD)-based cellular systems. We propose an interference cancellation technique using the concept of distributed antenna array. We show that the interference from the primary cellular system can be cancelled at a secondary node equipped with single antenna by introducing a helper that decodes the interference and transfers it to the secondary node. Interference is forwarded during the time periods in which training signals are transmitted within the primary cellular system. Since the duration of those intervals is short relative to periods for data transmission in the primary system, we introduce a scheme by which the helper compresses the interference before forwarding it. The performance advantage of our scheme is verified by computer simulation, where both analytical and measured channel models are used. The measurement data used in evaluations have been obtained through outdoor experiments while assuming a short-range secondary system. The results indicate that the proposed method for distributed interference cancellation leads to performance benefit, in particular under heterogeneous path loss conditions between the helper and the primary/secondary nodes.

Network coding is an effective method to improving relay efficiency by reducing the number of transmissions. However, its performance is limited by several factors such as packet length mismatch and rate mismatch. Although the former may be solved by re-framing, the latter remains a challenge and is likely to greatly degrade the efficiency of network coding. In this paper, we re-interpret network coding as a mapping of modulation constellation. On this basis, we extend such mapping to enable simultaneous use of different modulations by nesting the low-level constellation as a subset of the high level constellation. When relay links have different qualities, the messages of different flows are combined together in such a way that for each relay link its desired message is transmitted at its own highest rate. Compared with previous solutions to rate mismatch, the proposed scheme achieves the full rate of all relay links on the broadcast channel.

In this paper, a primary (licensed) user leases part of its resources to independent secondary (unlicensed) terminals in exchange for a tariff in dollars per bit, under the constraint that secondary transmissions do not cause excessive interference at the primary receiver (PRX). The PRX selects a power allocation (PA) for the secondary user that maximizes the secondary rate (and thus its revenue) and enforces it by the following mechanism: Upon violation of a predefined interference level, PRX keeps silencing randomly selected secondary users, until the aggregate secondary interference is below the required threshold. This mechanism ensures that secondary users may not be willing to deviate from the allocated PA. Specifically, the scenario gives rise to a Stackelberg game, in which the primary determines the PA and a Nash equilibrium (NE) constraint is imposed on the PA to ensure that secondary users do not have incentives to deviate, given their knowledge of the silencing mechanism run at the PRX. In principle, the primary should find the set of all PAs that are NE and among them choose the one that maximizes the aggregate secondary utility, and thereby the revenue of the primary. For the most general setting of channel gains, we investigate the conditions for NE for a subset of PAs. When the scenario is symmetric in the sense that all secondary users have the same channel gains in the direct/interfering links, we prove that only two optimal power allocations exist. Finally, for the case of general channel gains with strong interference, we show that there is a unique NE of the game.

This paper proposes bidirectional packet aggregation and coding (BiPAC), a packet mixing technique which jointly applies packet aggregation and network coding in order to increase the number of supportable VoIP sessions in wireless multi-hop networks. BiPAC applies network coding for aggregated VoIP packets by exploiting bidirectional nature of VoIP sessions, and largely reduces the required protocol overhead for transmitting short VoIP packets. We design BiPAC and related protocols so that the operations of aggregation and coding are well-integrated while satisfying the required quality of service by VoIP transmission, such as delay and packet loss rate. Our computer simulation results show that BiPAC can increase the number of supportable VoIP sessions maximum by around 70% as compared with the case when the packet aggregation alone is used, and 450% in comparison to the transmission without aggregation/coding. We also implement BiPAC in a wireless testbed, and run experiments in an actual indoor environment. Our experimental results show that BiPAC is a practical and efficient forwarding method, which can be implemented into the current mesh hardware and network stack.

Safety driving support is one of the most attractive applications of an inter-vehicle communications system. Real-time and reliable packet exchange among vehicles is a key to offering timely warnings to drivers in order to avoid fatal accidents. In this paper, we introduce the multi-carrier multi-code spread ALOHA (MM-SA) system, an inter-vehicle communications system developed for satisfying challenging requirements on supporting safety driving. MM-SA is based on code division multiple access (CDMA) technology, and has inherent robustness to the increase of node density as well as the hidden terminal problem. This paper presents an overview of MM-SA system including protocol design and prototyping as well as graphical user interface (GUI) tool, which are all developed for avoiding intersection collisions.

Network coding is an effective method to improve forwarding efficiency in multi-hop wireless networks. Previous network coding schemes proposed for unicast transmissions focus on scheduling where paths are already established, and assume a fixed rate for all links, neglecting link rate heterogeneity. In this paper we study a network coding based pseudo bidirectional relay scheme for wireless LAN, taking link quality into account. We first show when network coding based relay improves channel efficiency and how to select such a relay in a distributed way. Then we enhance network coding based transmissions from three aspects: (i) Coordinated rate adaptation is adopted to reduce the probability with which a priori packet is missing in times of network decoding. (ii) The retransmission scheduling completely solves the lack-of-a-priori problem. (iii) Piggybacking receiving status in ACK/NAK further enables opportunistic reception and avoids unnecessary transmissions. Simulation results confirm that compared with direct transmissions, the proposed relay scheme can reduce per-packet transmission time by up to 39% in Rayleigh fading environment.

A multi-player video game via wireless connections using portable devices is one of the most popular applications of ad-hoc networks. Broadcast transmissions can be used for many- to-many communications in multi-player games. However, reliable broadcast communications are hard to realize because of the lack of retransmissions in the medium access control (MAC) layer. In this paper, we propose a broadcast method using random linear network coding in order to enhance the reliability of many-to-many and real-time communications. Exploiting the periodic nature of game traffic as well as inherent robustness offered by random network coding, the proposed method can provide reliable packet deliveries between 2 nodes which have a link under constant fade or even under temporary loss. Our simulation results show that the proposed method can provide higher reliability than the other schemes using multi point relay (MPR) or redundant transmissions such as forward error correction (FEC). We also implement the proposed method in a wireless testbed, and show that the proposed method achieves high reliability in a real-world environment with practical degree of complexity when installed on current wireless devices.

This letter addresses a scheduling problem for wireless network coding (WNC). In our previous work, we have theoretically shown that the optimum number of nodes to be included into a network coded packet as well as its transmission rate depends on time varying link condition between a transmitting node and receiving nodes [1]. Based on this observation, this letter designs practical scheme which opportunistically selects scheduled nodes, packets to be coded and an employed modulation level according to time varying channel conditions and packet length. The numerical results show that the proposed opportunistic scheduling can improve the overall throughput as compared with non-opportunistic approach.

This paper proposes a novel interference cancellation technique using the concept of a distributed array, for the secondary use of the frequency resources in frequency division duplexing (FDD)-based cellular systems. In order to achieve efficient distributed interference cancellation, the secondary system exploit intervals for periodic training signals transmitted by FDD-time division multiple access (TDMA)-based cellular systems. We show that an efficient interference cancellation can be achieved by introducing helpers that decode the interference and transfer it to the secondary nodes. We take advantage of the high-speed links within the secondary system and devise a data compressing scheme that reduces time for transferring the decoded interference. We clarify the effectiveness of the proposed scheme by using computer simulation. As a parameter, the transmission quality between the helper and secondary nodes is varied. The results indicate that the proposed distributed interference cancellation is effective compared to a conventional adaptive array using a zero forcing algorithm, when the signal to noise ratio between the helper and the target secondary node is greater than 20 dB.

This paper studies various cooperative diversity schemes for orthogonal frequency division multiple access (OFDMA)- time division duplex (TDD) based two-hop cellular networks in low mobility scenarios, where the instantaneous channel state information is available at the base station. A user scheduling and radio resource allocation technique is developed in order to efficiently integrate various cooperative diversity schemes for the emerging IEEE 802.16j based systems. The analysis of the system with this scheduler shows that a simple cooperative diversity scheme which dynamically selects the best scheme between conventional relaying and direct transmission is promising in terms of throughput and implementation complexity. The conventional relaying refers to the scheme where the destination relies solely on the signals received through the relay.

This paper proposes a physical-layer security scheme for wireless networks, aiming to achieve communication secrecy by making the eavesdropper incapable of decoding the secret wireless message. The considered scenario features one user within the range of two access points, API and AP2. The APs are assumed to be connected through an alternative secure (e.g. wired) connection. The goal is to secure the wireless link between the user and API. While the user transmits to API, AP2 simultaneously transmits an interfering signal, which is a priori provided to API, such that API is likely the only node capable of decoding the user's entire transmission. Evaluation is done through simulation by measuring the upper bound of the information-theoretic secrecy and error performance. In the latter case it is shown that the eavesdropper experiences significantly higher error rates than the intended receiver, thus providing evidence of practical security.

It has recently been recognized that the wireless networks represent a fertile ground for devising communication modes based on network coding. A particularly suitable application of the network coding arises for the two-way relay channels, where two nodes communicate with each other assisted by using a third, relay node. Such a scenario enables application of physical network coding, where the network coding is either done (a) jointly with the channel coding or (b) through physical combining of the communication flows over the multiple access channel. In this paper we first group the existing schemes for physical network coding into two generic schemes, termed 3-step and 2-step scheme, respectively. We investigate the conditions for maximization of the two-way rate for each individual scheme: (1) the decode-and-forward (DF) 3-step schemes (2) three different schemes with two steps: amplify-and-forward (AF), JDF and denoise-and-forward (DNF). While the DNF scheme has a potential to offer the best two-way rate, the most interesting result of the paper is that, for some SNR configurations of the source - relay links, JDF yields identical maximal two-way rate as the upper bound on the rate for DNF.

This paper addresses a scheduling problem for wireless network coding which has been recently proposed as a novel method to enhance the throughput in wireless networks. The wireless network coding involves broadcast transmission of a network-coded packet which contains unicast data to several receiving nodes. These receiving nodes have time-varying fading links to the transmitting node, which can generate different instantaneous conditions for different links. In this paper, we introduce an opportunistic scheduling for such a wireless network coding, which selects a set of nodes whose packets are network - coded as well as the data rate for the broadcast transmission according to the instantaneous link conditions. We analyze the average capacity of such a scheduling, and discuss the impact of different parameters on the average capacity. We show that the opportunistic scheduling can maximize the average capacity by choosing the appropriate set of network-coded nodes according to the instantaneous link conditions. We also discuss the practical factors which can additionally affect the best scheduling strategy for wireless network coding.

In this paper, the possibility for a short-range cognitive radio (secondary communication system) to be located within the service area of the primary system is discussed. Although the secondary system interferes with the primary system, there can be certain locations in the service area of the primary system where the cognitive radio can reuse the frequency of the primary system without disturbing it or being disturbed by the primary system. We say that in those locations there is a spatial opportunity for communication in the secondary system. The primary and secondary systems have different features and usage scenarios, which result in different deployment conditions. This gives rise to differences between the path loss for a link in the primary system and the path loss for the interference from the primary to secondary systems. This paper investigates the impact of the heterogeneous path loss conditions on the spatial opportunity for the secondary system. Our approach can be applied as a general way to investigate the coexistence among multiple systems. We clarify that the change of the path loss coefficient due to the different antenna heights of the primary and secondary systems can largely affect the spatial opportunity for frequency reuse by the cognitive radios.

This paper addresses channel state information (CSI) estimation in a wireless relay network, which consists of a base station (BS), a relay station (RS), and a mobile station (MS). We propose a method for the BS to obtain the instantaneous CSIs of the three links (BS-RS, BS-MS, and RS-MS links) with minimized overhead. The CSI availability plays an important role for the BS to adapt its transmission strategies to the given channel conditions. Our proposed method exploits the fact that the link condition between fixed BS and fixed RS tends to be stable, and the frequent CSI update is not necessary for this link. In order for the BS to obtain the CSI of the distant link (i.e. RS-MS link), RS amplifies a pilot signal received from MS with a pre-defined amplification factor, and forwards it to BS. This enables the BS to obtain the CSI of the RS-MS link based on the received pilot signal and pre-knowledge on the CSI of BS-RS link. We show by computer simulation that our proposed method can reduce the required overhead for CSI estimation with little degradation on the accuracy of the obtained CSI.

Frequency Hopping (FH) technology has been widely used for short-range networks operating in unlicensed band. As the short-range FH networks gain momentum in ubiquitous usage, the interference that collocated FH networks cause to each other, termed self-interference, becomes one of the major sources that degrade the communication performance. This paper proposes the Adaptive Frequency Rolling (AFR), a particular adaptive instance of FH that enables FH networks to cooperate and effectively avoid the self-interference. The AFR uses as input solely the observed packet error rate (PER) and it does not require any exchange of information among the collocated networks. The effect of the AFR over a longer time interval is that the networks use the complete set of disposable channels in an implicit time-division and cooperative manner. The parameter choice is such that a network which uses AFR never occupies the channels in the unlicensed spectrum more than what is permitted by the current regulation. AFR is designed to be robust towards the noise-induced channel errors. We also design AFR with probing (AFR-P), a modified version of AFR, which can also overcome frequency-static interference from collocated non-FH network by introducing channel removal strategy with probing. Our simulation results show that AFR and AFR-P have superior goodput performance to pseudorandom frequency hopping (PFH), and also standard adaptive frequency hopping (AFH), where the latter is designed to exclusively combat frequency-static interference. All these features promote the great potential of AFR as a coexistence mechanism for unlicensed operation

In this paper, we propose a hybrid forwarding scheme for cooperative relaying in orthogonal frequency division multiplexing (OFDM) based networks. The proposed hybrid forwarding scheme changes the type of the forwarding scheme used by a relay terminal on a per sub-carrier basis. It adaptively decides to use either "Amplify and Forward (AF)" or "Decode and Forward (DF)" or "no relay" according to the instantaneous Signal to Noise Ratio (SNR) conditions between the source, relay and destination terminals. This decision is made based on analytically derived equations, which makes it possible to take into account all the link conditions in a relay network with low computational complexity. The bit error performance is presented for cooperative receive diversity with AF, with DF, with proposed hybrid forwarding scheme and for noncooperative transmission. Our results show that the proposed hybrid forwarding scheme significantly outperforms conventional cooperative relaying with AF and DF, and direct transmission schemes.

This paper considers relaying techniques that increase the achievable throughput in multi-hop wireless networks by taking advantage of the bi-directional traffic flow. Such a relaying technique is termed relaying with Bi-directional Amplification of Throughput (BAT-relaying). The BAT-relaying is utilizing the concept of anti-packets, defined for bi-directional traffic flows. The relay node combines the anti-packets that are destined for different nodes and broadcasts the combined packet. Two BAT-relaying techniques have been proposed previously, Decode-and-Forward (DF) BAT-relaying and Amplify-and-Forward (AF) BAT-relaying. While in DF the relay node combines the packets by an XOR operation, AF BAT-relaying utilizes the inherent packet combining provided by the multiple access channel. In an errorless channel, AF has always higher achievable throughput than DF, but in noisy channels the noise amplification can severely degrade the performance of AF. In this paper we introduce a new scheme for BAT-relaying, termed Denoise-And-Forward (DNF) BAT-Relaying. The DNF BAT-relaying also makes use of the combining provided by the multiple access channel, but it removes the noise from the combined anti-packets before broadcasting to the destinations. While in the noiseless channel DNF and AF offer the same throughput performance which is superior to DF BAT-relaying, in large regions of the lower SNR values DNF BAT-relaying has the best throughput performance of all three schemes. Due to the unconventional nature of the BAT-relaying schemes, there are many open issues for further investigation. The design of a practical DNF scheme concerns several protocol layers, including modulation and coding.

We address the problem of channel state information (CSI) feedback for scheduling the downlink (DL) data transmissions in a cellular system based on orthogonal frequency division multiple access (OFDMA). In order to benefit from multi-user diversity, the scheduler needs to know each user's CSI for each subchannel and time frame. However, this feedback information can become very high when the number of subchannels and/or users increase. Therefore, we have designed an adaptive feedback encoding method which can optimize the amount of feedback according to the variable amount of CSI requested by the base station (BS). The amount of useful CSI depends not only on the number of users, but also on the scheduling made at the BS. The simulation results show that with our adaptive encoding scheme, the performance of maximum CSI and proportional fair scheduling (PFS) with full CSI can be approached with a considerably reduced amount of feedback

This paper proposes a power control method for a hybrid duplexing scheme which has both time division duplex (TDD) and frequency division duplex (FDD) components. In the proposed method, the base station (BS) adaptively and continuously changes the transmission power for a mobile station (MS) whose transmission parameters have been scheduled by exploiting channel state information (CSI) obtained through channel reciprocity. The TDD component in hybrid duplexing makes it possible for the BS to exploit the channel reciprocity and the FDD component enables fast feed-back from MS to BS. By using the proposed power control method, the BS can quickly change the transmission power for a MS during a down-link (DL) frame. This counteracts the change in link condition due to MS mobility and/or burst interference (i.e. channel non-reciprocity problem). This allows the scheduling of BS made in the beginning of DL frame to be valid for the whole DL frame since the MS can experience almost constant link quality during a DL frame. Our simulation results show that the proposed power control method can significantly improve bit error rate (BER) performance.

In wireless networks, the shared broadcast medium enables interactions among nodes and thus introduction of novel communication modes. This paper introduces and analyzes relaying techniques that increase the achievable throughput in multi-hop wireless networks by taking advantage of the bi-directional traffic flow. Such a relaying technique is termed relaying with bi-directional amplification of throughput (BAT-relaying). The BAT-relaying is utilizing the concept of anti-packets, defined for bi-directional traffic flows. The relay node combines the packets (anti-packets) that are destined for different nodes and broadcasts the combined packet. The first variant, termed decode-and-forward (DF) BAT-relaying, has been proposed before in the literature. It combines the packets by using the XOR operation, which makes such proposal closely related to the network coding approaches. We proposed another type of BAT-relaying based on amplify-and-forward (AF), which utilizes the inherent packet combining that emerges from simultaneous utilization of a multiple access channel. We analyze the achievable throughput of the DF and AF BAT-relaying, regarding the impact of the traffic asymmetry and the channel errors. The unconventionality of this relaying, in particular AF BAT-relaying, opens many possibilities for further research

As the wireless personal area network (WPAN) gets utilized by more individuals, the interference that collocated WPANs cause to each other, termed self-interference, will be one of the major sources that degrade WPAN's communication performance. The conventional adaptive frequency hopping (AFH) strategies avoid frequency-static interference by reducing the hopset, but this deteriorates the performance if there is also self-interference. In this paper, we propose dynamic AFH (DAFH) mechanisms that are concurrently employed by collocated WPANs in order to avoid the self-interference. With DAFH, WPAN adaptively self-allocates a subset of frequency channels to be hopped, such as to minimize the experienced interference. The packet error rate is the only input to the proposed mechanisms, which enables DAFH to also avoid interference from frequency-static interferer. The optimization of the throughput should not be the sole target of the DAFH because WPAN operates in unlicensed spectrum and arbitrary adaptation of the FH pattern may be harmful to proximate non-WPAN devices. Therefore, we define and adopt an etiquette rule to characterize the behavior of the collocated WPANs with DAFH as a single collective entity that produces interference. The operation of DAFH is robust and adaptive to the dynamic changes in the environment and to the noise errors in the channel. Simulation results show that DAFH significantly increases the throughput of the WPANs in presence of both self-interference and frequency-static interference, while the WPANs employ best effort to minimize changes in the overall interference pattern

4G wireless communication networks are characterized by the need to support heterogenous terminals differing in size, display, battery, computational power, etc. For efficient usage of the wireless spectrum all devices should be served by the same spectrum instead of allocating spectra dedicated to the different terminal classes. This feature is naturally supported when the source coding of the traffic is done as a multiple description coding. The restoration quality of the information source is proportional to the quantity of the descriptors used in the restoration process. Hence, terminals with less capabilities may simply discard or not receive some of the descriptors, while high class terminals try to receive all information. In the case of partial reception of descriptors the performance can be improved by selection strategies for the descriptors. We advocate the usage of new descriptor selection schemes for multiple description coded services. The proposed schemes differ with respect to the availability of a feedback channel. All solutions are terminal oriented and are beneficial in the design of terminals that have robust and high quality services. Furthermore, our approaches inherently achieve fairness among different terminals. As an example of our results for video communication, we can show gains of 4 dB when the proposed approach is utilized in the system.

A Wireless Personal Area Network (WPAN) provides wireless links among proximate devices,usually carried by an individual.As WPAN gains momentum in ubiquitous usage, the interference that collocated WPANs cause to each other, termed self-interference, becomes one of the major sources that degrade the communication performance of WPAN. This paper in roduces the Frequency Rolling (FR), a particular instance of frequency hopping (FH) that enables he collocated WPANs to cooperate and avoid the self-interference. The FR uses as input solely the observed packet error rate (PER) and it does not require any exchange of information among he collocated WPANs. The effect of the FR over a longer time in erval is hat the WPANs use he complete set of disposable channels in an implicit time-division and cooperative manner. The parameters of he FR are chosen such that a WPAN which uses FR never occupies the channels in the unlicensed spectrum more than what is permitted by the current regulation. We compare the goodput offered by FR to the goodput of the collocated piconets when conventional pseudorandom FH is used. Our simulation results show that FR has superior goodput performance. In addition, he design of FR is made robust owards the errors due to the channel noise. Some guidance for practical fault-toleran design and future extensions of FR are given. All hese features promote the great potential of FR as a coexistence mechanism for unlicensed operation.

This paper discusses a modulation level selection method in software-based wireless multimedia communications system which employs adaptive modulation scheme. We propose a modulation level selection algorithm taking account of QoS (quality of service) for each service, and evaluate the performance by computer simulation. Our simulation results show that the proposed algorithm, which can reduce not only the number of required time slots but also the interference power for other users, improves the average delay performance as compared with the conventional one which only attempts to select higher modulation level with higher priority and to reduce only the number of required time slots.

We discuss data-link error control for reliable packet transmission in direct sequence code division multiple access (DS-CDMA) wireless communications systems. We analyze (transport control protocol) segment loss rate in a DS-CDMA system which employs selective repeat automatic repeat request (SR-ARQ) as the error control scheme with multicell environments. Our computer simulation results show that, in multicell environments, the improving effect of SR-ARQ on segment loss rate is small because of the burst frame error which is caused by intercell interference. Furthermore, we propose a method to overcome the burst frame error, and show that the method can significantly reduce segment loss rate.

We propose an uplink/downlink asymmetric slot allocation algorithm for CDMA/TDD-based wireless multimedia communications systems. We evaluate the average delay performance of the proposed algorithm by computer simulation, assuming a practical multicell environment and a multimedia service model which consists of several kinds of uplink/downlink symmetric and asymmetric services. Our simulation results show that the proposed algorithm, which can flexibly cope with uplink/downlink traffic asymmetry, improves the average delay performance as compared with symmetric slot allocation and fixed asymmetric slot allocation algorithms.

We propose two time slot allocation algorithms for code division multiple access with time division duplex (CDMA/TDD) systems to efficiently accommodate multimedia traffic. Assuming a practical multiple cell environment and a multimedia service model which consists of several kinds of circuit-switched and packet-switched services with different qualities of service (QoS), we evaluate the average delay of the CDMA/TDD system with the proposed algorithms, and compare the performance with that of CDMA with frequency division duplex (CDMA/FDD) and time division multiple access with TDD (TDMA/TDD) systems. Our computer simulation results show that the CDMA/TDD system with one of the proposed algorithms, which can effectively avoid interference among users with different QoS, can improve the average delay performance as compared with the other systems.