To Time Division Multiple Access Research Articles

TDMA Device Identification Using Continuity of Carrier Phase

Specific emitter identification provides the capability to distinguish radio emitters with the external features carried by the received waveforms. As existing features are not specific to time-division multiple access (TDMA) devices, it is yet intractable to discern the emitter in the case of low signal-to-noise rates or short durations. In this paper, we propose a novel characteristic based on the continuity of carrier phase and explore its application on TDMA device identification. The characteristic reflects a fact whether adjacent time slots are assigned to the same user terminal, which reveals a potential link between slots even if the protocol is unknown. To apply it to TDMA device identification, we augment the typical SEI scheme with two subsystems, Decision and Correction, in which the recognition results can be corrected to improve the accuracy. Simulation results demonstrate that the characteristic is resilient against the ambient noise, and it evidently improves the recognition accuracy.

The Capacity of Wireless CSMA/CA Networks

Due to a poor understanding of the interactions among transmitters, wireless networks using carrier sense multiple access with collision avoidance (CSMA/CA) have been commonly stigmatized as unpredictable in nature. Even elementary questions regarding the throughput limitations of these networks cannot be answered in general. In this paper, we investigate the behavior of wireless CSMA/CA networks to understand how the transmissions of a particular node affect the medium access, and ultimately the throughput, of other nodes in the network. We introduce a theory which accurately models the behavior of these networks and show that, contrary to popular belief, their performance is predictable and can be described by a system of equations. Using the proposed theory, we provide the analytical expressions necessary to fully characterize the capacity region of any wireless CSMA/CA network. We show that this region is nonconvex in general and agnostic to the probability distributions of all network parameters, depending only on their expected values. Our theory is also shown to extend naturally to time division multiple access (TDMA) networks and to predict how the network responds to infeasible input rates.

Convergence of Desynchronization Primitives in Wireless Sensor Networks: A Stochastic Modeling Approach

Desynchronization approaches in wireless sensor networks converge to time-division multiple access (TDMA) of the shared medium without requiring clock synchronization amongst the wireless sensors, or indeed the presence of a central (coordinator) node. All such methods are based on the principle of reactive listening of periodic “fire” or “pulse” broadcasts: each node updates the time of its fire message broadcasts based on received fire messages from some of the remaining nodes sharing the given spectrum. In this paper, we present a novel framework to estimate the required iterations for convergence to fair TDMA scheduling. Our estimates are fundamentally different from previous conjectures or bounds found in the literature as, for the first time, convergence to TDMA is defined in a stochastic sense. Our analytic results apply to the Desync algorithm and to pulse-coupled oscillator algorithms with inhibitory coupling. The experimental evaluation via iMote2 TinyOS nodes (based on the IEEE 802.15.4 standard) as well as via computer simulations demonstrates that, for the vast majority of settings, our stochastic model is within one standard deviation from the experimentally-observed convergence iterations. The proposed estimates are thus shown to characterize the desynchronization convergence iterations significantly better than existing conjectures or bounds. Therefore, they contribute towards the analytic understanding of how a desynchronization-based system is expected to evolve from random initial conditions to the desynchronized steady state.

On Outage Capacity in the Low Power Regime

This paper derives a formula for the wideband slope for outage capacity and consider its application to some specific wireless channels. For the broadcast channel, the formula indicates that superposition is always superior to time-division multiple access (TDMA). On the other hand, for the interference channel, we show that TDMA is better than superposition for most realistic situations.

Time transfer in impulse radio networks

The synchronization of clocks at physically separated network nodes requires timed signal exchanges between the nodes. Ultra-wideband (UWB) impulse signals potentially provide the means for doing this very accurately, but unlike narrowband signals, pulse signals are more naturally suited to time-division multiple-access (TDMA) schemes. In this work, we describe TDMA time-transfer schemes that estimate the mappings from a master node's clock time into slaves' clock times based on specific wireless measurements. We propose an optimal approach to distribution of UWB transmissions between those that perform alignment of nodes' clock rates and those that determine clock offsets. Analytical equations for the timing error variances are derived and our results suggest a possible lower bound for time-transfer error using UWB impulse signals.

Optical multiplexing technologies for access-area applications

This paper describes optical multiplexing technologies expected to be applied to access-area networks. First, these technologies are broadly categorized into wavelength-division multiplexing (WDM) and optical code-division multiple access (OCDMA), and possible variants are described in a comparison to time-division multiple access (TDMA). Next, their typical performances reported so far are overviewed in relation to the light sources utilized. While it is well known that WDM/OCDMA exhibits higher performance with laser sources, it is pointed that WDM/OCDMA with incoherent light sources are interesting alternatives for access-area applications. Two multiplexing methods that use incoherent light sources are introduced in more detail; one is spectrum-sliced WDM and the other is coherence-multiplexed CDMA. After the introduction of transmission experiments, their performance limitations are discussed

On The Tradeoff Between Two Types of Processing Gain

One of the features characterizing almost every multiple access (MA) communication system is the processing gain. Through the use of spreading sequences, the processing gain of Random CDMA systems (RCDMA), is devoted to both bandwidth expansion and orthogonalization of the signals transmitted by different users. Another type of multiple access system is Impulse Radio (IR). In many aspects, IR systems are similar to time division multiple access (TDMA) systems, and the processing gain of IR systems represents the ratio between the actual transmission time and the total time between two consecutive ransmissions (on-plus-off to on ratio). While CDMA systems, which constantly excite the channel, rely on spreading sequences to orthogonalize the signals transmitted by different users, IR systems transmit a series of short pulses and the orthogonalization between the signals transmitted by different users is achieved by the fact that most of the pulses do not collide with each other at the receiver. In this paper, a general class of MA communication systems that use both types of processing gain is presented, and both IR and RCDMA systems are demonstrated to be two special cases of this more general class of systems. The bit error rate (BER) of several receivers as a function of the ratio between the two types of processing gain is analyzed and compared under the constraint that the total processing gain of the system is large and fixed. It is demonstrated that in non inter-symbol interference (ISI) channels there is no tradeoff between the two types of processing gain. However, in ISI channels a tradeoff between the two types of processing gain exists. In addition, the sub-optimality of RCDMA systems in frequency selective channels is established.

On Strategies of Multiuser MIMO Transmit Signal Processing

In this letter, we introduce five different strategies of linear transmit signal processing for multiuser multiple-input multiple-output (MIMO) systems and provide performance comparisons in terms of maximum throughput in both uncorrelated and correlated channels when the number of transmit antennas is much larger than the number of receive antennas. It is shown that the multiuser MIMO schemes are preferable to time-division multiple-access (TDMA)-based MIMO schemes, hence demonstrating the power of multiuser MIMO signal processing. Our work also indicates possibilities for future research in finding efficient suboptimal algorithms. As an example, we show that our multiuser MIMO decomposition scheme can improve the maximum throughput compared to TDMA-based MIMO schemes for large number of transmit antennas or high transmit power.

Orthogonal frequency‐division multiple access and its application to CATV networks

AbstractWe introduce the concept of orthogonal frequency‐division multiple access (OFDMA) and investigate its application to send upstream information from subscriber premises to the cable head‐end in cable TV (CATV) networks. The carrier and timing synchronizations needed to ensure orthogonality between different subscriber signals are achieved by sending common pilot signals from the head‐end. Whereas N demodulators are required to accommodate N simultaneous users in conventional FDMA systems, OFDMA only requires a single demodulator followed by an N‐point discrete Fourier transform (DFT). We analyze the performance of this technique and compare it to time‐division multiple access (TDMA) which appears in several international standards. Our results indicate that OFDMA is an attractive multiple access technique which offers increased robustness to narrowband interference, impulse noise, and other signal impairments which characterize typical CATV networks.

The role of satellites in personal communication services

This paper aims at providing a complete analysis of the issues relevant to satellite systems in the perspective of the third generation of mobile systems. The analysis considers, on the one hand, the possible satellite system evolutionary paths and, on the other hand, the satellite system requirements related to technological issues. As regards the satellite evolutionary paths, the paper provides a view of the satellite systems already in operation or currently being developed and outlines the guidelines followed by future satellite systems (in that respect, particular emphasis is given to small satellites). The analysis is performed by also taking into account the potential market and the regulatory issues. As regards the satellite system requirements related to technological issues, some key features such as integration with the terrestrial cellular networks, satellite system capacity, handover, synchronization, are discussed in the light of the technological innovations which are being proposed for the third generation of mobile systems. The above-mentioned issues are dealt with by referring both to time division multiple access (TDMA) and to code division multiple access (CDMA), i.e., the third-generation candidate access techniques. >

Intersymbol interference reduction for differential MSK by nonredundant error correction

A theoretical analysis and experimental results for differential detection of minimum-shift keying (MSK) with nonredundant error correction are described. The proposed demodulator utilizes the output detected from the difference in phase over two or three time slot intervals along with the conventional detector output. A single error can be corrected by using two differential detectors, and a single and a double error can be corrected by using three detectors. It is shown that the error rate performance is improved, especially in the presence of intersymbol interference (ISI), without the addition to the transmitted data of redundant bits. Simulation and experimental results agree with the theoretical analysis, which shows that the degradation of differential detection relative to coherent detection is reduced from 2.2 dB without error correction to 1.2 dB with single error correction and to 0.7 dB with double error correction. The method can be applied effectively to mobile communications over a fading channel or to time-division multiple-access (TDMA) communications using burst mode transmission.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>