Modeling Channel Access Delay and Jitter of IEEE 802.11 DCF

With the ever-increasing requirement of WLAN to support real-time services, it is becoming important to study the delay properties of WLAN protocols. This paper constructs a new model to analyze the channel access delay and delay jitter of IEEE 802.11 DCF in saturation traffic condition. Based on this analytical model, average channel access delay and delay jitter are derived for both basic access and RTS/CTS-based access scheme. The accuracy of the analytical model is validated by simulations and furthermore we discuss the impact of initial contention window, maximal backoff stage, and packet size on channel access delay and delay jitter of 802.11 DCF using the proposed model.

Robust Packet Video Transport Over Wireless Fading Channels Using a Joint Source-channel Coding Approach

In this paper, we address the problem of robust video transmission over wireless networks. Specifically, we consider packet video transmission over wireless IP networks based on the RTP/UDP/IP protocol stack. Digital video delivered over wireless networks is expected to suffer quality degradation from both packet loss and bit errors in the payload. In this paper, both packet loss and bit errors in the payload are considered and the performance of a joint source-channel coding (JSCC) approach employing forward error-correction (FEC) coding schemes for H.263 +  video transmission is studied. Results indicate that with an appropriate JSCC approach, FEC-based error-control techniques can significantly improve the packetization efficiency for a given end-to-end quality requirement and lead to more acceptable video delivery quality over time-varying wireless networks. Another important observation is that with a JSCC approach the fading effects of wireless links upon end-to-end video quality are substantially decreased compared to a system without using channel coding, resulting in attractive robust performance characteristics.

IP Transmission over TETRA Packet Data Service: Simulation and Measurement Results

This paper evaluates the packet data performance of Internet Protocol (IP) over TErrestrial Trunked RAdio (TETRA), focusing on the effects of packet size and message transmission rate. We performed a range of simulations to evaluate the average packet delay and packet failure probability corresponding to IP datagram transmission on the Packet Data CHannel (PDCH) in a TETRA cell. We employed IP packets of different sizes and we considered a number of different scenarios with respect to the number of users in a cell and datagram transmission rate. The simulation results offer TETRA operators the means for facilitating network planning and optimization of datagram-based services. Apart from the simulation, we also conducted an extensive measurement survey on the performance of IP over the TETRA PDCH. In particular, we carried out measurements in a client–server communication scenario with different datagram sizes and typical user mobility and radio propagation conditions. Measurement results include throughput, delay jitter, percentage of lost datagrams and out-of-order datagrams. The results obtained through our measurement survey can extent and enhance the simulation results because they are more realistic and consider user mobility as well as channel impairments.

A Study on Ultra Low-Latency Mobile Networks

Traffic demand for real-time services as well as non real-time services has recently been increasing, due to the rapid improvement in transmission bit-rate within communication networks. In the future ubiquitous network society, in addition to traffic demand for user-to-user real-time communications services, traffic of real-time applications is set to explode due to new communications traffic for machine-to-machine communications. This paper proposes “ultra low-latency mobile networks,” where the target value for unidirectional end-to-end latency per IP packet is 10 ms, in order to establish a new communications infrastructure capable of providing next-generation real-time services. This paper introduces a model of such ultra low-latency mobile networks and the results of a feasibility study are also presented. The simulation study shows the potential to realize a mobile network with ultra low-latency of less than 10 ms for IP packets and a low IP packet error rate of  < 0.1% through simulations. A test-bed developed to measure actual latency is also introduced in this paper as well as measurement results using this test-bed. The measurement results also confirm the possibility indicated by the simulation studies.

Design and Evaluation of DNS as Location Manager for HIP

Host Identity Protocol (HIP) is designed to provide secure and continuous communication by separating the identifier and locator roles of the Internet Protocol (IP) address. HIP also has efficient solutions to support host mobility. In this paper, we propose a location management scheme based on Domain Name System (DNS) for HIP. In the proposed scheme, a new DNS HIP resource record is used to translate a domain name into a host identity tag and an IP address. We also develop an analytical model to study the performance of DNS as location manager in terms of success rate, which takes into account the velocity of mobile nodes, the radius of a subnet, the regional network size, the packet transmission delay between the mobile node and the rendezvous server, and the packet processing delay at the DNS and the rendezvous server. The performance results show that for a reasonable range, the DNS is a feasible solution for location management with high success rate for HIP.

A route maintaining algorithm using neighbor table for mobile sinks

In the wireless microsensor networks, both source and sink nodes can be changed or mobile. The movement of source and sink may lead to the breakage of existing routes. In most routing protocols, query packets are broadcasted to correct a broken route between source and sink, which causes significant communication overhead in terms of both energy and delay. In order to support the sink mobility of conventional routing protocols, we propose a simple route maintaining algorithm which does not use the flooding method. Since the proposed algorithm does not require the information on the geometric location of sensor nodes, it can be easily adopted in most existing routing protocols including Ad Hoc On Demand Distance Vector (AODV) and Direct Diffusion (DD). Experimental results show that the proposed algorithm drastically improves the conventional routing protocols in terms of both energy and delay in case of mobile sinks.

Cluster-Based Autoconfiguration for Mobile Ad hoc Networks

IP address autoconfiguration of mobile nodes is highly desirable in the practical usage of most mobile ad hoc networks (MANETs). This paper proposes cluster-based autoconfiguration, a novel approach for the efficient address autoconfiguration of MANETs. The cluster structure derived from clustering techniques is used to manage address assignment and conflict resolution. By introducing the concept of virtual address agents (AAs), the proposed approach can be applicable to many existing clustering protocols. Finally, analysis and simulation demonstrate that the proposed scheme outperforms the previous autoconfiguration approaches.

Information-based connection algorithm for supporting QoS in nested mobility network

A multihop mobile wireless network can be a collection of wireless mobile nodes forming a temporary network without the aid of any established infrastructure or centralized administration. Mobile nodes communicate with each other using multihop wireless links. Each mobile node in the network also acts as a router, which forwards data packets to other nodes. A main challenge in the design of this mobile network is the development of dynamic routing protocols that can efficiently find routes between two communicating nodes that often change the network topology drastically and unpredictably. All communications between the nodes inside the mobile network and the global Internet must be maintained, although the mobile router (MR) connecting the other mobile network to the global Internet must change their address; and mobile nodes suffer from end-to-end delay and handoff delay. That is to say, hereafter the packets sailing for the mobile node would not be routed directly for the destination, but will always make a detour by way of HA to the target node. In this paper, we suggest Information-based Connection Algorithm that adds keyword management method in order to resolve such a problem, simulations are carried out with NS-2 for performance evaluation. The results of the simulations show an improvement on throughput and handoff delay, and consequently the QoS improvement.

A novel fault-tolerant multi-EPON system with sharing protection through bridge ONUs

In the EPON, any failure of optical line terminal (OLT) or feeder fiber can halt the entire system. Many previous studies proposed dedicated protection architectures to protect the critical components, which results in high cost for deployment. To achieve high reliability and low-cost for deployment, this article proposes a novel fault-tolerant Multi-EPON system with cost-effective shared protection through Bridge ONUs. Under failures, the Bridge ONU controls the faulty EPON, plays the role of OLT and the transmission of faulty EPONs are restored by relaying to other interconnected adjacent EPONs. The minimum hop-count relay algorithm and the relay window mechanism are also proposed for the Multi-EPON system to efficiently help data relaying to the central office (CO). Furthermore, the one-wait dynamic bandwidth allocation enables the controller of affected Passive Optical Networks (PONs) to obtain more up-to-date buffer information from each ONU in order to enhance overall system performance. The simulation results show that the proposed Multi-EPON system can provide high system performance for different failure situations in terms of throughput, average delay, maximum delay, and expedited forwarding (EF) jitter, especially in high traffic loads.

Multilayer traffic engineering for multiservice environments

Multilayer traffic engineering (MLTE) serves to provide cross-layer online network optimization techniques to cope with rapid variations and short-term evolutions in traffic patterns. MLTE extends traffic engineering as it exists in IP/MPLS-based technology toward the multilayer IP/MPLS-over-optical transport network. In addition to the IP/MPLS traffic routing, MLTE exposes much larger adaptation flexibility by building on next-generation automatic switched optical transport networks. These offer fast setup and teardown of end-to-end multi-hop optical connections (lightpaths), which are offered to the IP/MPLS layer as dynamically provisioned capacity. This dynamic nature leads to an IP/MPLS logical topology that can be reconfigured on the fly, and IP/MPLS link capacity that can be up- or downgraded as client traffic demand varies. These MLTE techniques are generally used to increase perceived network performance in terms of throughput or QoS. As such, a MLTE-managed network offers a better than best-effort service. Many types of traditional and novel services are shifting toward IP/MPLS technology. Consequentially, MLTE algorithms and strategies should be conceived with the characteristics of such services in mind. We present a MLTE strategy that can be implemented in a robust and distributed way. This strategy is then taken as the starting point in a study which evaluates its suitability to such services. We show how the strategy can be adapted considering service performance metrics such as end-to-end delay, traffic loss, and routing stability, and how such service optimizations impact general MLTE objectives such as IP/MPLS logical topology mesh size reduction.

Methods for Compression of Feedback in Adaptive Multi-carrier 4G Schemes

In this paper, several algorithms for compressing the feedback of channel quality information are presented and analyzed. These algorithms are developed for a proposed adaptive modulation scheme for future multi-carrier 4G mobile systems. These strategies compress the feedback data and, used together with opportunistic scheduling, drastically reduce the feedback data rate. Thus the adaptive modulation schemes become more suitable and efficient to be implemented in future mobile systems, increasing data throughput and overall system performance.

Improving performance of TCP over mobile wireless networks

Mobile IP is a network layer protocol for handling mobility of hosts in the Internet. However, mobile IP handoff causes degradation of TCP performance. Hence, there is a need for improving performance of TCP over mobile IP in wireless mobile networks. We propose an approach which handles losses due to both wireless link errors and host mobility. To handle losses due to host mobility, a method for seamless handoff is proposed. Empirical results show that the scheme provides substantial improvement of performance.

On the Performance of Broadband Mobile Internet Access System

In this paper, we evaluate the performance of OFDMA/TDD-based broadband mobile internet access system with the features of adaptive modulation & coding (AMC) and hybrid ARQ. We present a framework of system-level simulation and furthermore, intend to derive the insightful results towards understanding the performance of broadband mobile internet access system. The average system throughput as well as delay performance is evaluated for the different channel characteristics and system parameters, which allows for predicting the system capacity in the varying cellular network environment.

Channel Adaptive Power Control in the Uplink of CDMA Systems

In this paper, we propose an adaptive power control algorithm using optimal control theory for CDMA cellular systems. With linear quadratic control, each mobile transmits to achieve a desired SIR under the fast varying environment of practical CDMA cellular systems. We apply Kalman filter theory to estimate a channel variation which is vulnerable to nonconstant link gain, mutual interference and uncertain noise. Through simulation comparison with DCPC algorithm, the suggested power control algorithm shows an increased uplink channel capacity.

Test Compression for IP Core Testing with Reconfigurable Network and Fixing-Flipping Coding

This paper proposes a class of test compression for IP (intellectual property) core testing. The proposed compression requires only test cubes for the IP cores and it dose not require the structural information about the IP cores. It uses both a reconfigurable network and classes of coding, namely fixing-flipping coding and fixing-shifting-flipping coding. The proposed compression is evaluated from the viewpoint of compression rates and hardware overhead. For three out of four large ISCAS89 benchmark circuits, the compression rates of the proposed compression are better than those of the four existing test compressions.

Noise-Insensitive Digital BIST for any PLL or DLL

PLLs are the heart of most SoCs, so their performance affects many tests. Practical, published PLL BIST approaches cannot measure <10 ps RMS jitter or >1 GHz. This paper describes how a SerDes undersampling DFT technique was adapted to test multiple PLLs and DLLs for jitter, phase error, output frequency, duty cycle, lock time, and lock range. Two techniques for cancelling random and systematic noise are also described. The multi-GHz range, sub-picosecond jitter noise floor, and minimal silicon area are better than for any previous silicon-proven DFT or BIST that needs no calibration or analog circuitry. FPGA implementation results are provided.

Master Interface for On-chip Hardware Accelerator Burst Communications

We explain a systematic way of interfacing data-flow hardware accelerators (IP) for their integration in a system on chip. We abstract the communication behaviour of the data flow IP so as to provide basis for an interface generator. Then we measure the throughput obtained for different architectures of the interface mechanism by a cycle accurate bit accurate simulation of a SoC integrating a data-flow IP. We show in which configuration the optimal communication scheme can be reached.

A Novel GPS-free Method for Mobile Unit Global Positioning in Outdoor Wireless Environments

This paper investigates a Global Positioning system (GPS)-free positioning method for mobile units (MUs) in outdoor wireless environments by using the Bayesian filtering formulation. The procedure utilizes simulated inertial measurements, cell-ID of the serving base station, and pre-determined locations grouped according to cell antennas radio coverage in the experimentation area. The developed algorithm makes no assumptions on the initial position of the MU. However, the algorithm takes some time to converge. Experiments show the range of inertial measurement errors that would maintain reliable location information with accuracy comparable to GPS positioning.

Minimum delay routing for wireless networks with STDMA

STDMA emerges as a promising channel access technique for providing Quality of Service (QoS) guarantees in multi-hop ad hoc networks such as community mesh and sensor networks. The contention-free channel access combined with spatial reuse of the channel provide significant benefits in the energy/throughput trade-off. On the other hand, the time-multiplexed communication introduces extra delay on the packets when relayed by intermediate nodes. Hence in large wireless sensor networks or mesh networks, where data is routed over several hops before reaching the data sink, STDMA protocols may introduce high end-to-end latency due to the reservation-based access policy. We argue that a suitable routing protocol specifically designed for reservation-based Medium Access Control (MAC) protocols can alleviate their high-latency drawback. Following this argument, we propose first such routing algorithms working on top of a generic STDMA MAC protocol. First, we consider routing with data fusion and present our GreenWave routing idea. We show that our algorithm significantly reduces the end-to-end delay when compared to routing over the shortest-hop paths. Second, we consider routing without data fusion, by taking into account the effect of congestion along the paths on the end-to-end delays. We provide a QIP formulation of the problem, and present a lower bound and a heuristic algorithm to bound the optimal solution. Based on the centralized heuristic algorithm, we propose a distributed, dynamic routing protocol GreenWave routing with Congestion and Flow control (GWCF), which uses a novel congestion and flow control technique utilizing the underlying contention-free protocol. We show by simulations that GWCF routing significantly improves the end-to-end delay while increasing the network throughput when compared to routing over shortest paths.

A New Routing Metric for Satisfying Both Energy and Delay Constraints in Wireless Sensor Networks

Besides energy constraint, wireless sensor networks should also be able to provide bounded communication delay when they are used to support real-time applications. In this paper, a new routing metric is proposed. It takes into account both energy and delay constraints. It can be used in AODV. By mathematical analysis and simulations, we have shown the efficiency of this new routing metric.