Analytical Analysis of Applying Packet Fragmentation Mechanism on Both Basic and RTS/CTS Access Methods of the IEEE 802.11b DCF Network Under Imperfect Channel and Finite Load Conditions

The mathematical modeling and performance evaluation of the IEEE 802.11 network in all its various extensions (802.11b, 802.11a, 802.11g, 802.11e, 802.11n, etc.) have already been widely explored over the past years. However, the Packet Fragmentation Mechanism (PFM), which is proposed by the IEEE work group to enhance the MAC sub-layer of the IEEE 802.11 standard in an error-prone channel, has been missed in the available literature. Yet, the PFM is the only existing solution to reduce the influence of bit error rate and the length of data packets on the packet error rate, and consequently on the performances of IEEE 802.11 networks. In this paper, we propose a new three-dimensional Markov chain in order to model, for the first time in the literature, the PFM in both Basic and RTS/CTS access methods of the IEEE 802.11b DCF network under imperfect channel and finite load conditions. Then, we develop mathematical models to derive a variety of performance metrics, such as: the overall throughput, the average packet delay successfully transmitted, the average packet drop time, the delay jitter and the packet delay distribution. Performance analysis of applying PFM on both Basic and RTS/CTS access methods of the IEEE 802.11b DCF network under imperfect channel and finite load conditions shows original results and leads to new conclusions that could not be intuitively expected.     

STUDY OF RADIO DEVICES ON 2.4GHZ SM BAND IN PHYSICAL PHASE

In the unlicensed 2.4GHz ISM band, there is not only IEEE 802.11 wireless systems being used, but also some other devices, such as residential microwave oven, Bluetooth devices, and cordless phone. All these devices that are not used for the data communications cause unintentional interference that will degrade the WI-FI system. In this paper, the transmission powers for common RF devices are measured and the SIR （signal-to-interference ratio） of different interferers to Wi-Fi is also studied. With this information, the effect of different interference on WI-Ft signal can hence be quantified. Furthermore, the ability of the interference avoidance protocols, which is built into the AP, to address interference problems caused by that device is determined.     

Performance Analysis of Capture Effect in High Speed Wireless Networks

The influence of capture effect on the high speed wireless networks is investigated in this paper. A new garkov chain model considering capture effect for the binary exponential back-off scheme in the MAC layer has been proposed. A new throughput model used in the IEEE 802.11 networks is proposed Based on this new Markov chain model, and then we analyzed throughput impacted by the capture effect under different transmission speeds. The performance analysis shows the capture effect has more impact on the throughput of high speed wireless networks than that on the low speed wireless networks.     

Performance Investigation of IEEE 802.11e EDCA Under Non-Saturation Condition Based on the M/G/1/K Model

The IEEE 802.11e network provides different with QoS （Quality of service） guarantee for different traffic streams. The Enhanced distributed channel access （EDCA） in IEEE 802.11e MAC protocol is proposed to support prioritized QoS on the basis of the Distributed coordination function （DCF） in IEEE 802.11. We first build a new Markov chain model for the EDCA. The model takes into account both the idle state that represents that there are no packets to be transmitted and differentiation based on different AIFS-value （Arbitration inter-frame space） for different traffic. We can use the signal transfer function of the generalized Z-transform domain state transition diagram to derive a probability distribution of the MAC layer service time and analyze the performance of EDCA from a non-saturated channel to a saturated medium by using M/G/1/K queuing model. The proposed model is calculated numerically and validated against simulation results, we observed a good match between the analytical model and simulation. Simulation and theoretical results show that despite providing prloritized QoS, the EDCA still can not support strict QoS for real-time application. On the other hand, it is inevitable that there is unfairness of channel access to prloritized traffic due to EDCA.     

P-Zone： Connectivity-based Packet Path Tracing in Wireless Sensor Networks

In large-scale Wireless sensor networks （WSNs）, the network status is complex and unpredictable, which brings great challenges to practical network design and management. Tracing the route path of each data packet in the network is an important way to observe network behaviors and understand network dynamics. However, tracing the full route path of each packet could be highly challenging, due to the hard resource con- straint in WSNs. Our previous work proposes a hash-based path tracing mechanism, and leverages network connectivity and node locations to reduce the computational complexity. However, the node locations may be unavailable in some scenarios. In this work, we further propose a location-free enhancement to the hash-based path tracing mechanism, called P-Zone. P-Zone requires only network connectivity information to reduce the computational complexity. Theoretical analysis and practical simulations are conducted to evaluate the effectiveness and performance of our design. The results indicate that P-Zone can significantly reduce the computational complexity of the hashbased path tracing mechanism, while effectively tracing the full route path of each packet in the network in a real-time manner, and outperforms the state-of-the-art methods.     

Dynamic Per-flow Queuing to Reduce Competitions Among Large Number of Flows

Per-flow queuing is believed to be able to guarantee advanced Quality of service （QoS） for each flow at high speed routers. With the dramatic increase for both llnk speed and number of traffic flows, per-flow queuing confronts a great challenge, since millions of queues need to be maintained for implementation in a traditional sense. In this paper, setting only a small number of physical queues, we propose a Dynamic per-flow queuing （DPFQ） mechanism that achievesthe same performance as per-flow queuing at a cost of an additional Binary content addressable memory （BCAM）. The proposed mechanism works due to the fact that the number of simultaneous active flows at a mini-time scale in the router buffer is much smaller than that of in-progress flows. In DPFQ, a physical queue is created on demand when a new flow comes, and released when the flow temporarily pauses or finishes. A small BCAM is occupied to map flows to queues, so as to guarantee that only the packets from the same flow are buffered in any assigned queue. Through analysis and simulation we show that using a small number of physical queues, DPFQ achieves both low operation delay and power consumption.     

Performance analysis of the IEEE 802.11 MAC protocol for wireless LANs

Wireless local area networks (WLANs) are extremely popular being almost everywhere including business, office and home deployments. The IEEE 802.11 protocol is the dominating standard for WLANs. The essential medium access control (MAC) mechanism of 802.11 is called distributed co‐ordination function (DCF). This paper provides a simple and accurate analysis using Markov chain modelling to compute IEEE 802.11 DCF performance, in the absence of hidden stations and transmission errors. This mathematical analysis calculates in addition to the throughput efficiency, the average packet delay, the packet drop probability and the average time to drop a packet for both basic access and RTS/CTS medium access schemes. The derived analysis, which takes into account packet retry limits, is validated by comparison with OPNET simulation results. We demonstrate that a Markov chain model presented in the literature, which also calculates throughput and packet delay by introducing an additional transition state to the Markov chain model, does not appear to model IEEE 802.11 correctly, leading to ambiguous conclusions for its performance. We also carry out an extensive and detailed study on the influence on performance of the initial contention window size (CW), maximum CW size and data rate. Performance results are presented to identify the dependence on the backoff procedure parameters and to give insights on the issues affecting IEEE 802.11 DCF performance. Copyright © 2005 John Wiley & Sons, Ltd.     

Adaptive Packet Classification Algorithm Based on IXP2800 Network Processor

Packet classification is a critical data-plane task for modern routers to support value-added services, especially for those requiring QoS and flow based processing. However, classification at 10Gbps or higher using an algorithmic approach is still challenging. New generation of Network processor unit （NPU） provides unprecedented processing power for network applications, and it opens a new venture to explore thread-level parallelism for attacking networking performance bottlenecks. This paper studies the implementation issues of how an adaptive clas- sification algorithm can be efflciently implemented on a multi-core and multithreaded NPU architecture. Our algorithm combines best traits of Recursive flow classification （RFC） algorithm and bitmap compression technique to achieve deterministic classification performance while keeping the memory growth checked. When mapping such an algorithm onto the Intel IXP network processor, we consider the characteristic of IXP architecture early in the algorithm-design phase to eliminate the potential perfor- mance bottlenecks. The implemented algorithm is highly efflcient and it can run at 10Gbps speed or higher on a real IXP2800 chip.     

The On-line Calibration Technology of System Delay Based on Dynamic Delay Cancellation for Generalized TT＆C Channel Simulator

An on-line system delay calibration method based on dynamic cancellation for generalized high-precision Tracking, telemetry and command （TT＆C） channel simulator is proposed. This method manages to estimate the time-varying system delay in real time through the coupling signal of input signal and simulated output signal, and then modifies the simulated parameters by the estimated value. With this method, it effectively avoids the effect of time-varying system delay caused by temperature drift, aging of components and other factors on high precision simulation. In this paper, the dynamic cancellation technology, which is the kernel and foundation of this method, is presented to eliminate the simulated motion law between the input signal and output signal. The time delay estimation method based on cross correlation and area barycenter arithmetic is introduced to estimate the time-varying system delay. The simulation results show the validity and high-precision performance.     

Time Delay Estimation Based on Entropy Estimation

Abstract--This paper presents a novel time delay estimation （TDE） method using the concept of entropy. The relative delay is estimated by minimizing the estimated joint entropy of multiple sensor output signals. When estimating the entropy, the information about the prior distribution of the source signal is not required. Instead, the Parzen window estimator is employed to estimate the density function of the source signal from multiple sensor output signals. Meanwhile, based on the Parzen window estimator, the Renyi＇s quadratic entropy （RQE） is incorporated to effectively and efficiently estimate the high-dimensional joint entropy of the multichannel outputs. Furthermore, a modified form of the joint entropy for embedding information about reverberation （multipath reflections） for speech signals is introduced to enhance the estimator＇s robustness against reverberation.     

EDCA/CA: Enhancement of IEEE 802.11e EDCA by Contention Adaption for Energy Efficiency

This paper presents a Contention Adaptation (CA) mechanism to improve the energy efficiency in IEEE 802.11e EDCA. By suspending some transmissions, the proposed EDCA/CA can reduce the number of collisions. Because unnecessary retransmissions are eliminated, the energy consumption is reduced. Extensive simulations have been performed to demonstrate the performance of the proposed EDCA/CA. The results show that EDCA/CA can reduce the energy consumption significantly. It reduces frame delay as well when traffic load is heavy. When traffic load is light, the proposed EDCA/CA will slightly increase the video delay, which in general is still acceptable. Furthermore, the proposed EDCA/CA is simple and easy to implement. It is fully compatible with the 802.11e EDCA. It is both effective and practical.     

Personal Area Networks: Bluetooth or IEEE 802.11?

Interconnecting all our electronic devices we carry around, such as cellular phones, PDAs, and laptops, with wireless links requires a cheap, low-power radio technology that still delivers good performance. In this context, the Bluetooth wireless technology was developed to meet the requirements introduced by these personal area networks (PANs). However, today we see a widespread deployment of wireless local area network (WLAN) radios (primarily IEEE 802.11b) also in small devices, such as PDAs. This paper will compare the PAN capabilities of a Bluetooth-based system with an IEEE 802.11b-based system. In order to focus the comparison on link and networking functionality, the IEEE 802.11b radio is assumed to be operating at the same power level as the Bluetooth radio (i.e., assuming a 0 dBm radio). Results are obtained by means of simulations in which throughput and delay are measured for multihop and overlaid PANs. Estimations on power usage are also given in the simulations. The results indicate that as the number of PANs increases, the Bluetooth-based PANs basically maintain the same bandwidth per PAN, while the corresponding IEEE 802.11-based PANs suffer significantly from the increased co-channel interference. However, for cases with a few co-channel-interfering PANs (2-3 PANs hosting about 10-15 nodes), the IEEE 802.11b-based PANs offer a higher bandwidth per user than the corresponding Bluetooth PANs, which corresponds to the difference in link bandwidth between the two systems. At high interference levels, the Bluetooth PAN offers a higher capacity than the IEEE 802.11 PAN. The latter also shows unfairness among TCP connections in the PAN at high loads. The energy efficiency, defined as successfully transmitted bits per energy unit, decreases sharply for IEEE 802.11 with increased number of PANs, while Bluetooth maintains a constant level. Packet delays are also shown to be more stable for the Bluetooth PAN than for the IEEE 802.11 PAN as the number of PANs increases.     

Wideband Direction of Arrival Estimation with Linear Array： Analysis and Closed-Form Formulae

To estimate the Direction-of-arrival （DOA） of a far-field wideband source using a linear array, the Time-difference-of-arrlval （TDOA） based and Steered- response power （SRP） algorithms are of the most useful. In this paper, for white Gaussian signal and noise, the esti- mation variances of both the methods and the Cramer-Rao lower bound （CRLB） are derived in closed-form for a lin- ear array. Meanwhile, a Gauss-Markov （GM） procedure is introduced to achieve optimal conversion of the estimated delay vectors for the TDOA based estimator. Moreover, a generalized SRP estimator is proposed for the generalized case with nonuniform SNR.     

288×4 Time Delay and Integration Readout IC for Infrared Focal Plane Array

A new structure of 288×4 CMOS Time delay and integration （TDI） readout integrated circuit is presented in this paper. The TDI function is implemented using an integration and storage circuit array and a charge amplifier with the advantages of low power and compact layout. An experimental chip has been designed and fabricated in a 0.5μm double-poly-three-metal CMOS technology. The bi-directional TDI, defective element deselection and two-gain option （1.015pC/2.03pC） functions have been realized in the experimental chip and the measurement results at liquid nitrogen temperature indicated that all functions were correct and the performance has satis- fied the requirement of long waveform IRFPA. The readout speed of each output can reach 5MHz and the dynamic range is 75.6dB.     

A Novel Generalized Simulation Technology of Aerospace TT＆C Channel

A novel generalized simulation method is proposed to simulate the dynamic transmission delay of wideband and arbitrary signal in aerospace Tracking, telemetry and command （TT＆C） channel. This method orthogonally demodulates the wideband and arbitrary Radio-frequency （RF） signal into complex baseband by a Local oscillator （LO） signal. Then the method of dynamic interpolation and delay reconstruction is proposed to ob- tain the delay reconstruction signal of complex baseband signal based on the variation rules of satellite-to-earth loca- tion. Meanwhile, the method of satellite-to-earth distance subsection and polynomial fitting is applied to obtain the delay reconstruction signal of LO signal. The simulated output signal is achieved through the synthesis of two de- lay reconstruction signals mentioned above. The proposed method can accurately simulate the variation characteris- tics of time delay and Doppler when wideband and arbi- trary RF signal transmits in channel, without knowing any priori knowledge, such as signal form, signal parameters, and so on.     

An Advanced Effective Capacitance Model for Calculating Gate Delay Considering Input Waveform Effect

In deep submicron designs, predicting gate delay time is a noteworthy work for Static Timing Analysis. The effective capacitance Ceff concept is usually used to calculate the gate delay with interconnect loads. Conventionally, the input-signal to the gate is always assumed as a ramp waveform. However, the input signal is also the output of CMOS gates with interconnect loads and not the ramp waveform. Thus the simple assumption as a ramp signal results in significant influence on the delay calculation. In this paper, an advanced effective capacitance model is proposed to consider both the input waveform effect and the interconnect loads, where the nonlinear influence of input waveform is modeled as one part of the effective capacitance for calculating the gate delay. Experimental results show a significant improvement in accuracy when the input waveform effect is considered.     

A 55 nm CMOS △∑fractional-N frequency synthesizer for WLAN transceivers with low noise filters

A fully integrated ΔΣ fractional-N frequency synthesizer fabricated in a 55 nm CMOS technology is presented for the application of IEEE 802.11b/g wireless local area network(WLAN) transceivers.A low noise filter,occupying a small die area,whose power supply is given by a high PSRR and low noise LDO regulator,is integrated on chip.The proposed synthesizer needs no off-chip components and occupies an area of 0.72 mm2 excluding PAD.Measurement results show that in all channels,the phase noise of the synthesizer achieves -99 dBc/Hz and -119 dBc/Hz in band and out of band respectively with a reference frequency of 40 MHz and a loop bandwidth of 200 kHz.The integrated RMS phase error is no more than 0.6°.The proposed synthesizer consumes a total power of 15.6 mW.     

Out-of-Band Signaling Scheme for High Speed Wireless LANs

In recent years, the physical layer data rate provided by 802.11 Wireless LANs has dramatically increased thanks to significant advances in the modulation and coding techniques employed. However, previous studies show that the 802.11 MAC operation, namely the distributed coordination function (DCF), represents a limiting factor: the throughput efficiency drops as the channel bit rate increases, and a throughput upper limit does indeed exist when the channel bit rate goes to infinite high. These findings indicate that the performance of the DCF protocol will not be efficiently improved by merely increasing the channel bit rate. This paper shows that the DCF performance may significantly benefit from the adoption of two separate physical carriers: one devised to manage the channel access contention, and another devised to deliver information data. We propose a scheme, referred to as out-of-band signaling (OBS), designed to reuse (and remain backward compatible with) the existing 802.11 medium access control (MAC) specification. Performance evaluation of OBS is carried out through analytical techniques validated via extensive simulation, for both saturation and statistical traffic conditions. Numerical results show that OBS improves the throughput/delay performance, and provides better bandwidth usage compared with the in-band signaling technique employed by DCF.     

CCK demodulation via symbol decision feedback equalizer

A symbol decision feedback equalization (DFE) technique is developed for demodulating complementary code keying (CCK) signals. The efficacy of the proposed receiver is demonstrated on the physical layer (PHY) specified in the IEEE 802.11b wireless local area network (WLAN) standard. Packet error rate (PER) performance is compared with that of the conventional RAKE receiver. The proposed receiver structure and its low complexity variations demonstrate significant performance advantages over the RAKE receiver, especially in severe multipath channels. While a large delay spread can limit the performance of two low-complexity variations discussed here, performance of the optimal symbol DFE receiver is not limited by delay spread as long as the channel signal-to-noise ratio (SNR) is sufficiently high.