Donald C. Cox's research while affiliated with Stanford University and other places
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Publications (58)
An admission and congestion control scheme is proposed for large-scale wireless mesh access networks that stabilizes the network under heavy traffic loads within a cooperative and distributed medium access control framework. The scheme utilizes only local information available at the controlling router, and yet guarantees to deliver the data of the...
In practical applications, some coded symbols are unequally punctured for rate matching of terminated convolutional codes. In this letter, performance upper bounds are proposed for a terminated convolutional code punctured with an arbitrary pattern. To obtain the upper bounds, a weight enumerator is defined to represent the relation between the Ham...
A medium access control (MAC) protocol is developed for time division multiple access (TDMA) and time division duplex (TDD)-based large wireless mesh networks (WMNs) with infrastructure support. Utilizing control time slots, the protocol operates in a fully cooperative and distributed manner: mesh routers cooperate to negotiate resource allocation,...
In coded OFDM systems, the transmission power of each subchannel is the same. In this letter, a power optimization scheme is presented to minimize FER or BER of a coded OFDM system under constant transmission power constraint. The power optimization is shown to be a convex optimization problem.
Parallel processing is a promising technique for reducing the execution time of a large and complex wireless network simulation. In this article, a parallel processing technique is presented for time-driven simulations of large and complex wireless networks. The technique explicitly considers the physical-layer details of wireless network simulator...
There is a continuing quest for increasing the data transmission rate in wireless systems. Cellular mobile radio systems have advanced from second generation digital technology with limited data capability to third generation systems with data transmission rates on the order of a few megabits per second and on to fourth generation systems with goal...
A control time slot assignment protocol is developed for time division multiple access (TDMA) and time division duplex (TDD)-based large wireless mesh networks (WMNs). Through the protocol, each wireless mesh router acquires a broadcast time slot that supports a minimum average signal-to-interference-plus-noise ratio (SINR) to all of its neighbors....
There is continuing effort to increase the data transmission rate in evolving wireless systems. These evolving wireless systems include cellular mobile systems and wireless local area networks (WLANs). However, because of the complexity of these systems, it appears that fundamental physical relationships between transmission rate and the range over...
In this paper we consider the design of a robust timing synchronization algorithm for pilot-aided OFDM systems in high-mobility fading environments. We first analyze the impact of both mobility and timing errors on the performance of a pilot-aided OFDM system for frequency selective fading channels, by deriving an expression for channel estimation...
In this paper we are interested in designing a robust timing synchronization algorithm for OFDM systems that utilize pilot-aided channel estimation. We first characterize the impact of timing errors on the performance of a pilot-aided OFDM system. We derive analytical expressions for average channel estimation error variance in the presence of timi...
In orthogonal frequency division multiplexing (OFDM) systems, carrier frequency offset (CFO) due to mismatch of the local oscillators causes inter-carrier interference (ICI), which may result in significant performance degradation. Although, several frequency synchronization schemes were reported, there possibly remains frequency offset and it can...
Orthogonal Frequency Division Multiplexing (OFDM) in combination with bit-interleaved coded modulation (BICM) is efficient and robust high-speed transmission technique used in IEEE 802.11a standard. In this paper, using Request To Send (RTS)/ Clear To Send (CTS) mechanism, we present a method to improve throughput performance by adaptively changing...
In this letter, we propose tight performance upper bounds for convolutional codes terminated with an input sequence of finite length. To obtain the upper bounds, a weight enumerator is defined to represent the relation between the Hamming distance of the coded output and the Hamming distance of the input bits of the code. The upper bounds on frame...
In this paper, we propose tight performance upper bounds for convolutional codes terminated with an input sequence of finite length. To obtain the upper bounds, a generalized weight enumerator of single error event is defined to represent the relation between the Hamming distance of the coded output and the Hamming distance of the selected input bi...
Using parallel processing, the execution time of wireless network simulations can be significantly decreased without compromising the fidelity of the simulation. However, incorporating details such as signal propagation, interference, and resource allocation schemes may add considerable complexity to the parallel simulation which may overshadow the...
The capacity advantage of multiple input-multiple output (MIMO) channels lays in the decomposition of the channel into several spatial sub-channels. Knowledge of the channel at the transmitter can further increase the system capacity. This effect has been theoretically demonstrated. Here we illustrate the potential of channel state information (CSI...
This letter addresses the effect of timing synchronization errors that are introduced by an erroneous detection of the start of an orthogonal frequency-division multiplexing (OFDM) symbol. Throughout this letter, the term "timing error" would refer to this type of error. Such errors degrade the performance of an OFDM receiver by introducing interca...
With the rapid growth of the Internet and other Internet protocol-related applications, wireless systems have shifted toward supporting a wider variety of data services. This has placed an enormous strain on the already tight capacity of wireless systems. Many improvements have been made at the link layer in second- and third-generation wireless sy...
A new model for UHF propagation in large buildings is presented. This model relies on knowledge of the interior arrangement of the building without requiring much detail. The guiding of radiation along hallways is the most significant propagation process at distances of more than 10 m from the transmitter. The waveguide model predicts the power los...
Systems with multiple element transmitter and receiver arrays have been shown to achieve very high spectral efficiencies. The theoretically achievable Shannon capacity is a function of the channel between the transmitters and the receivers. On the simulation level, one assumes certain statistical characteristics for the channel, but on a practical...
Waveguide analysis is used to predict power levels received in a microcellular system in an urban environment. An Urban street with tall buildings on both sides is modeled by a plate parallel waveguide made of rough plates. The distribution of power among the waveguide modes tends to concentrate in the low order modes, at large distances from the s...
Multiple-input-multiple-output (MIMO) systems can provide high data rate wireless services in a rich scattering environment. We study one of the proposals for MIMO systems, the Bell Labs Layered Space-Time (BLAST) architecture. Channel estimation using training sequences is required for coherent detection in BLAST. We apply the maximum-likelihood c...
We analyze the behavior of a multiple element antenna system in an indoor environment based on the measurements taken in the Lucent Bell Labs building in Crawford Hill, NJ, with a system of 12 transmitters and 15 receivers. In particular, we investigate the capacity behavior with respect to the polarization of the transmitting/receiving elements an...
Radio frequency radiation in urban areas, emanating from a source lower than the surrounding buildings, propagates along streets. Urban streets with tall buildings on both sides are modeled as hollow slab waveguides made of lossy plates. The facade of the buildings is taken into account by introducing roughness onto the waveguide walls, which cause...
In the context of heterogeneous networks and diverse communication devices, real person-to-person communications can be achieved with a Universal Personal Identification (UPI) that uniquely identifies an individual and is independent of the access networks and communication devices. Hierarchical mobility management techniques (MMTs) have been propo...
In the context of heterogeneous networks and diverse communication devices, real person-to-person communication can be achieved with a universal personal identification (UPI) that uniquely identifies an individual and is independent of the access networks and communication devices. Hierarchical mobility management techniques (MMTs) have been propos...
The future of cellular wireless networks could see multihop transmission through relays as a means of improving performance of existing cellular systems. Incorporating intermediate relays is the first step in an evolution of wide area wireless information networks (see Pahlavan, K. and Levesque, A. H., 1995; Naghshineh, M., 1999) from the extreme o...
We express signal correlation in a waveguide in terms of waveguide modes. We investigate the effect of waveguide dimensions, element location and attenuation on transmitter and receiver correlation. An analytical approach for the calculation of the signal correlation is proposed, and the results are verified with simulations. Good agreement is achi...
A new method is presented for estimating the mobile speed and the
average received power in general wireless propagation environments. The
locally stationary received signal is expanded in a local exponential
basis using best basis methods of wavelet analysis. An estimate of the
time-varying Doppler power spectrum is obtained together with an
estim...
Handoff algorithms are used in wireless cellular systems to decide
when and to which base station to handoff. Traditional handoff
algorithms generally cannot keep both the average number of unnecessary
handoffs and the handoff decision delay low. They do not exploit the
relative constancy of path loss and shadow fading effects at any given
location...
This paper presents measurement results that demonstrate the
different propagation characteristics of the vertical and horizontal
polarizations and their crosscorrelation coupling under line-of-sight
and non-line-of-sight conditions. We also present a simplified model for
the propagation environment that uses an approach similar to the method
of im...
A derivation is provided for the mean and variance of the local maxima of a Rayleigh fading envelope. The calculation is performed for a uniform 2-D angular distribution of incident power using the autocorrelation function given in the book by Jakes (1974). This calculation is useful to obtain estimates of the mean received signal strength over a g...
In this paper, we propose a dual mode blind equalizer based on the
constant modulus algorithm (CMA). The blind equalizer is devised for
short burst transmission formats used in many current wireless TDMA
systems as well as future wireless packet data systems. Blind
equalization is useful for such short burst formats, since the overhead
associated w...
In the context of heterogeneous networks and diverse communication
devices, real person-to person communication can be achieved with a
universal personal identification (UPI) that uniquely identifies an
individual and is independent of the access networks and communication
devices. In this paper, we propose two location management techniques
(LMTs)...
With the evolution of analog mobile wireless communications
systems into digital second- and third-generation systems, there is
growing interest in finding more efficient ways of managing the
available resources, in particular radio spectrum and power. In the
context of time division multiple access (TDMA) systems, this interest
has led to the deve...
A new technique is described for estimating the speed of a mobile
station in a wireless system. The mobile speed maps the characteristic
spatial scale of the received signal into a characteristic temporal
scale. The continuous wavelet transform tracks changes in the temporal
scale to estimate the mobile speed as a function of time. This technique
r...
Good estimates of local mean signal power level are needed by
wireless cellular systems for use in channel access, power control and
handoff. Many systems today use weighted sample average estimators which
are not optimal in Rayleigh fading environments. The optimal local mean
signal level estimator for the Rayleigh fading environment is derived
an...
Handoff is the procedure by which a user's radio link is transferred between radio ports in the network without an interruption of the user connection. In this paper, we discuss how a Wireless Asynchronous Transfer Mode (ATM) network may reroute a user connection during a handoff. We propose a novel procedure called "Nearest Common Node Rerouting (...
This paper provides an alternative to using SVCs by enabling the use of permanent virtual circuits (PVCs) for overlay signaling and avoiding the signaling overhead associated with SVC setup. Three network architectures to enable use of PVCs in the overlay signaling are discussed and a comparative analysis of these three architectures is presented....
Increasing demand for wireless mobile communications, coupled with limited network resources, has motivated investigation into alternative efficient mobility management solutions. In this paper, we consider wireless PCS call setup protocols. We propose a Lightweight Location Lookup Protocol, which significantly reduces the network signaling and set...
This paper presents a framework for modeling and evaluating the performance of location management schemes for a Personal Communication Services (PCS) network. The models take into account complex human behaviors, and are based on actual measurements of these behaviors. Real measurements are a crucial factor in achieving realistic performance evalu...
More than a factor of three increase in overall personal
communication system (PCS) capacity can be achieved in small handheld
communication devices with limited battery power or in small
low-complexity base stations when incorporating simple interference
cancellation techniques without training sequences in the channel-access
algorithm that realiz...
In wireless cellular systems, handoff algorithms decide when and
to which base station to handoff. Traditional handoff algorithms
generally cannot keep both the average number of unnecessary handoffs
and the handoff decision delay low. They do not exploit the relative
constancy of path loss and shadow fading effects at any given location
around a b...
A new technique for initializing an adaptive equalizer is proposed
and analyzed. This technique, called synthetic initialization,
synthesizes additional training symbols from a training sequence. The
training sequence is thus effectively lengthened without any additional
transmission overhead. Synthetic initialization can be used with any
adaptive...
This paper presents a new protocol for controlling access to the shared radio medium in a multi-tier wireless ATM network. A multi-tier Wireless ATM network provides seamless connectivity to the users in multiple geographic environments ranging from local area networks to wide area wireless networks. Dynamic Resource Allocating Media Access (DRAMA)...
This paper presents a novel location management technique, HOPPER, that is designed to support in a scalable and efficient manner nongeographical (lifelong) personal numbers in Personal Communications Services (PCS). Performance comparisons between our scheme and other schemes are derived from large scale simulations using a realistic traffic model...
A multiple decision delay decision-feedback equalizer (MDDDFE) is proposed for short-burst data communication over frequency-selective Rayleigh-fading indoor wireless channels. Simulation results show that MDDDFE can maintain low average bit error rate without incurring too much computational overhead. In particular, approximately 3dB gain over the...
We propose a method to eliminate the bias term present in the
timing-error estimator employed in digital receivers where the input
signal is sampled by a fixed clock which is not synchronized to the
transmitter clock. This bias error results from the nonideal
interpolation that precedes the timing-error estimator. We show that it
can be derived as...
We consider the problem of managing the information required to locate users in a wireless communication system, with a focus on designing and evaluating location management techniques that are efficient, scalable, and flexible. The three key contributions of this paper are: (1) A family of location management techniques, HiPER (for Hierarchical Pr...
The world of wireless telecommunications is rapidly changing. The capabilities of wireless networks are improving at a steady pace. This paper presents a protocol implementation for implementing mobility in an Asynchronous Transfer Mode (ATM) network. The vision of the authors is of one "ATM-based wireless telecommunications network" that is capabl...
This article presents a realistic teletraffic modeling framework
for personal communications services. The framework captures complex
human behaviors and has been validated through analysis of actual call
and mobility data. Using the proposed framework, a large-scale
simulation was performed on a model of the San Francisco Bay area.
Simulation resu...
In a high capacity personal communication system (PCS), for a given bandwidth, co-channel interference (CCI) limits the system capacity. Low-complexity diversity combining algorithms and circuit architectures for co-channel interference cancellation and frequency-selective fading mitigation, which do not require training sequences, are introduced....
A new method for estimating the frequency of a complex sinusoid in complex white Gaussian noise is proposed. Its computational complexity is comparable to Kay's method [1989], but it attains the Cramer-Rao bound (CRB) down to lower signal-to-noise ratio (SNR) values. Simulation results are included to demonstrate the performance of the proposed met...
Several loop applications of wireless technology are aimed at reducing the cost of deploying communications services ranging
from telephone to wideband video. In these applications, wireless links replace a portion of a wireline loop from a central
location (a central office or cable headend) to a subscriber. The replacement of labor-intensive wire...
We propose a novel symbol-by-symbol selection diversity approach with adaptive DFE's. The branch decision with the maximum estimated a posteriori probability of correct is selected as final and used to adapt the DFE for all branches. Simulations show an improvement of 3.5dB over a previously proposed selection diversity scheme. 1 Introduction Indoo...
The explosive growth in wireless communications systems and the demand for advanced mobility features have created novel data management problems. Current schemes to address these problems rely on database organizations that have limited functionality and performance anomalies. We propose a new data management scheme that is flexible and scalable,...
This article attempts to identify different issues and to put many
of the activities in wireless into a framework that can provide
perspective on what is driving them, and perhaps even yield some
indication of where they appear to be going in the future. The
technologies and systems that are currently providing, or are proposed
to provide, wireless...
Abstract Models of radio propagation are indispensable in the design and analysis of wireless communication,systems. They are used to predict power and interference levels and analyze other properties of the radio link. Guidance of radio waves along urban streets is a well known phenomenon;,a similar effect takes place along indoor hallways. We
Citations
... Optimal performance, see e.g., [111], is achieved if the signals from each branch are uncorrelated and can be coherently combined with each branch's weight factor proportional to its signal to interference ratio. Diversity has also been shown to decrease the effect of inter-symbol interference and co-channel interference [41,127]. Of importance for quality-based fixed-step power control, studied in chapter 7, is that diversity decreases the duration and depth of fading dips. ...
... Zone 3 (light-blue colored in Figure 2c) is under NLoS conditions caused by buildings. The position of buildings can generate a corridor-configuration at some street segments, where the waveguide effect [44,45] is produced. The average RSS fluctuates between −100 dBm and −120 dBm. ...
... A large time-driven wireless mesh network simulator has been created that implements realistic physical layer characteristics such as radio propagation and co-channel radio interference, and captures the stochastic network behavior due to random traffic arrivals, admission control, and queuing. The simulator employs a novel parallel processing technique to reduce the long runtimes developed by the authors in [16], [17] running over a compact supercomputing platform comprising 32 AMD Opteron 64-bit processors interconnected by multigigabit Infiniband interconnect links and having 2 gigabytes of memory associated with each processor. ...
... Örneğin yüksek hızda veri paketi indirme bağlantısı (High Speed Downlink Packet Access, HSPDA) haberleşme sisteminde kısa olan kontrol mesajları katlamalı kodlar ile korunurken, uzun olan veri paketleri Turbo kodlar ile korunur [17]. Varolan FEC yapısından daha iyi SNR eşik değerine sahip, ses kalitesini ve haberleşme menzilini arttıran, AMBE 3600 bps vocoder FEC yapısının yerini alabilecek nitelikte olan [23,12] Golay kod [18,19] ve 5/6 delikli katlamalı koddan (Punctured Convolutional Code, PCC) [20] oluşan melez bir FEC planı önerilmiştir. Önerilen FEC planı AMBE 3600 bps vocoder'da hâlihazırda kullanılan FEC planına karşın 2,95 dB kodlama kazancı sağlamıştır. ...
... The routing protocol employed by the WMN is then described including its operations and routing metrics. Two ACC policies, one denoted as AC RO and considered in [36] and in Section 4.8.3 and the other denoted as AC RF and considered in [37] and in Section 4.8.4, are then presented including their stability properties. ...
... combating the burst errors stemming from the OFDM frequency selectivity that compromises the channel coding performance [14]. ...
... It is worth mentioning that acceleration of high-fidelity wireless communication simulations has been investigated through geography-based partitioning for parallel implementation on multiple processors as well [20]. However, parallel computing is not the focus of this work. ...
... Control slots also provide a means for access router to exchange control messages among themselves without error for such operations as network discovery, routing table construction and resource negotiation. The network employs the control time slot assignment protocol presented in [6], through which each wireless AR acquires a broadcast time slot that supports a minimum average signal-to-interference-plus-noise ratio (SINR) over the first control subslot (tBUSY inFig. 2) to all of its neighbors. ...
... Printed antennas are very used in wireless and mobile communications which gives easy access for telecommunication devices. For this purpose frequency bandwidths are available to meet this need especially 5G [1,4]. DGS technique has been required for many applications due to their advantages for printed antennas of bandwidth, gain and omnidirectional radiation pattern [7]. ...
... To improve the receiver performance, post-FFT tracking is useful to mitigate the remaining CFO [22] . Although this residual is small, it degrades the receiver performance due to the accumulated phase rotation consequences along each OFDM symbol in the packet [28] . On the assumption that the CFO is compensated earlier, it is worth eliminating its phase rotation effect. ...
