Time Division Multiple Access Wireless Research Articles

Wireless TDMA‐Based Body Area Network Platform Gathering Multibiosignals Synchronized with Patient’s Heartbeat

In the application of a body area network in medical healthcare, the process of receiving, archiving, and analyzing multibiosignals simultaneously from different devices for each body is very important. For example, to diagnose sleep apnea symptoms, a patient must sleep with dozens of devices, including electroencephalography (EEG), electrocardiogram (ECG), photoplethysmogram (PPG), peripheral oxygen saturation (SpO2), nasal cannula, and bands. Various wireless methods of body area network for acquisition and measurement of body signals have been introduced, but it is difficult to accurately diagnose various biosignals because their measurement frequencies are different from each other, and they are not guaranteed precise synchronization. Because each body biosignal is commonly synchronized with the heartbeat of the patient, precise synchronization of the heartbeat and other measuring cycles of each device is a critical attribute for analyzing the corelation of each biosignal in the body area network. However, it is difficult to guarantee the precise synchronization of multibiosignals by solely using carrier sense multiple access with collision detection‐ (CSMA/CD‐) based wireless protocols, which are mainly used in existing body area networks. This study proposes a method of creating a self‐organizing body area network based on wireless Time Division Multiple Access (TDMA) to guarantee the synchronization of multibiosignals and compare its accuracy with the CSMA/CD method.

Estimating the number of users in TDMA networks based on redundancy of adaptive channel coding

Blind identification of protocols in wireless communication networks is a critical subject in non-cooperative context. In this paper, a novel method is proposed to estimate the number of active users (NoAU) in wireless time division multiple access (TDMA) networks based on the redundancy of adaptive channel coding. The proposed method, which is based on decision trees and machine learning, can also be used in adaptive coding systems to identify the number of distinct code rates employed by a single transmitter. Simulation results show that the proposed method can estimate the number of codes with accuracy around 99% in noiseless situation. Moreover, for noisy environments, reasonable accuracies compared to naïve methods are obtained.

Aircraft Strain WSN Powered by Heat Storage Harvesting

The combination of ultra-low-power wireless communications and energy harvesting enables the realization of autonomous wireless sensor networks. Such networks can be usefully applied in commercial aircraft where wireless sensing solutions contribute to weight reduction and increased ease of installation and maintenance. This paper presents, for the first time, a complete energy-autonomous wireless strain monitoring system for aircraft. The system is based on a multimode wireless time-division multiple access (TDMA) medium access control (MAC) protocol that supports automatic configuration and a time-stamping accuracy better than 1 ms. The energy supply depends solely on an innovative thermoelectric energy harvester, which takes advantage of the changes in environmental temperature during takeoff and landing. The system was successfully integrated and passed the functional and flight-clearance tests that qualify it for use in a flight-test installation.

Opportunistic Routing and Scheduling for Wireless Networks

In spatial time division multiple access wireless mesh networks, not all links can be activated simultaneously, as links scheduled for transmission must satisfy the specified SINR requirements. Previously, slot assignment has been done on a link basis, where a set of links is selected for transmission in a given slot. However, if selected links are in deep fade or have no traffic to transmit, the slot is wasted. Thus, a node-based scheme was proposed, where a set of nodes is selected for transmission. Which link to be used by a node depends on the links’ instantaneous traffic load. Although this allows us to exploit multi-user diversity, it creates a planning discrepancy: slot assignment is designed based on long-term channel statistics, but scheduling on short-term channel fading conditions. Consequently, the performance gain of the node-based scheme is not consistent: it is marginal under certain scenarios. To avoid the design discrepancy, we develop a new slot-assignment and routing framework in this paper. The new approach incorporates short-term channel fading statistics to optimize the long term slot assignment, routing and scheduling simultaneously. Hence, multi-user diversity can be exploited more efficiently. Not only is the performance gain of the resulting system significant (can be as much as 64% higher throughput than the scheme introduced by Chen and Lea), it is also less topology dependent compared with the one by Chen and Lea.

Energy Efficiency Cross Layer Protocol for Wireless Mesh Network

Wireless mesh network (WMN) is a novel emerging technology that will change the world more effectively and efficiently. It is regarded as a highly promising technology being increasingly important in mobile wireless networks of the future generation. In this paper, we consider energy management for wireless mesh networks from a point of view that started recently to attract the attention means the conservation of energy for operational and the environment reasons which is known as the Green Networking. This paper discusses different routing protocols to establish a protocol which considers energy efficiency. The existing protocols are compared using the basic functions of routing and the suggest protocol is designed to overcome some of their shortcomings. We are focusing on the conception of the cross-layer routing protocol that is implemented in TDMA (Time Division Multiple Access) wireless mesh networks based MAC protocol.

Optimal joint routing and link scheduling for real-time traffic in TDMA Wireless Mesh Networks

We investigate the problem of joint routing and link scheduling in Time-Division Multiple Access (TDMA) Wireless Mesh Networks (WMNs) carrying real-time traffic. We propose a framework that always computes a feasible solution (i.e. a set of paths and link activations) if there exists one, by optimally solving a mixed integer-nonlinear problem. Such solution can be computed in minutes or tens thereof for e.g. grids of up to 4×4 nodes. We also propose heuristics based on Lagrangian decomposition to compute suboptimal solutions considerably faster and/or for larger WMNs, up to about 50 nodes. We show that the heuristic solutions are near-optimal, and we exploit them to gain insight on the schedulability in WMN, i.e. to investigate the optimal placement of one or more gateways from a delay bound perspective, and to investigate how the schedulability is affected by the transmission range.

Link Scheduling Algorithms for Wireless Mesh Networks

Wireless Mesh Networks (WMNs) have the potential of being a cost effective solution to provide connectivity and coverage in both urban and rural areas. Typically, a WMN is a backbone network that carries high data rate traffic and employs Time Division Multiple Access (TDMA) like access mechanisms. For a WMN to provide high throughput, the design of an efficient link scheduling algorithm is of paramount importance. Towards this end, we provide an overview of link scheduling algorithms in Spatial TDMA wireless mesh networks. These algorithms can be classified into three categories: those based only on a communication graph model of the network, those based on a communication graph model and Signal to Interference and Noise Ratio (SINR) threshold conditions at receivers and those based on an SINR graph model of the network. We first outline a framework for modeling STDMA networks. We review representative research works and provide the description of an algorithm from each of these classes. We describe the relative merits and demerits of each class of algorithms and compare their performance via simulations. We conclude with a discussion on practical implementation of these algorithms and open research problems.

Delay Aware Link Scheduling for Multi-Hop TDMA Wireless Networks

Time division multiple access (TDMA) based medium access control (MAC) protocols can provide QoS with guaranteed access to the wireless channel. However, in multi-hop wireless networks, these protocols may introduce scheduling delay if, on the same path, an outbound link on a router is scheduled to transmit before an inbound link on that router. The total scheduling delay can be quite large since it accumulates at every hop on a path. This paper presents a method that finds conflict-free TDMA schedules with minimum scheduling delay. We show that the scheduling delay can be interpreted as a cost, in terms of transmission order of the links, collected over a cycle in the conflict graph. We use this observation to formulate an optimization, which finds a transmission order with the min-max delay across a set of multiple paths. The min-max delay optimization is NP-complete since the transmission order of links is a vector of binary integer variables. We devise an algorithm that finds the transmission order with the minimum delay on overlay tree topologies and use it with a modified Bellman-Ford algorithm, to find minimum delay schedules in polynomial time. The simulation results in 802.16 mesh networks confirm that the proposed algorithm can find effective min-max delay schedules.

Reverse link erlang capacity of time-hopping/TDMA wireless communication systems

In this paper, the performance analysis of a recently proposed multiple-access (MA) scheme for data communication via TDMA wireless channel in terms of Erlang capacity is carried out. The proposed MA scheme takes advantage of time-hopping (TH) within multiple frames of a time-division multiple-access (TDMA) system to provide access to the channel for network subscribers. First, a super-frame for the TDMA signaling is defined. Subsequently, a user is provided with an access code that is used to hop over the indicated TDMA super-frame, hereafter referred to as a TH frame. The assignment codes are those of the {0,1} family codes, recently exploited for fiber-optic code-division multiple-access (FO-CDMA) applications. It is assumed that each assignment code can guarantee no more than 1 hit in a superframe and that code synchronization exists between all users. For differential phase-shift-keying (DPSK) and M-ary frequency-shift-keying (MFSK) modulated THMA systems and when side information is available at the receiver, upper bounds on the overall symbol error rate are derived when the communication channel is impaired by slow frequency non-selective Rayleigh and Rician fading. The capacity of the proposed system is obtained in terms of Erlang/sector for reverse link and is compared to those of TDMA and CDMA systems. It is demonstrated that the power control requirement of the proposed THMA system is identical to that of a conventional TDMA system, and that the proposed system achieves an Erlang capacity identical to that of its CDMA counterpart

ORCA-MRT: an optimization-based approach for fair scheduling in multirate TDMA wireless networks

This paper presents an optimization-based approach to solve the wireless fair scheduling problem under a multirate time division multiple access (TDMA)-based medium access control (MAC) framework. By formulating the fair scheduling problem as an assignment problem, the authors propose the optimal radio channel allocation for multirate transmission (ORCA-MRT) algorithm for fair bandwidth allocation in wireless data networks that support MRT at the radio link level. The key feature of ORCA-MRT is that while allocating transmission rate to each flow fairly, it keeps the interaccess delay bounded under a certain limit. The authors investigate the performance of the proposed ORCA-MRT scheduler in comparison to another recently proposed multirate fair scheduling algorithm. They also propose two channel prediction models and perform extensive simulations to investigate the performance of ORCA-MRT for different system parameters such as channel state correlation, number of flows, etc.

Channel estimation and interference suppression for space–time coded systems in frequency‐selective fading channels

AbstractIt is of great interest to provide high data rate services in wireless communication systems. In order to support such services, it is desirable to extend space‐time (ST) coding, originally proposed for known, frequency‐nonselective fading channels, to unknown, multipath channels. In this paper, we consider the problem of interference suppression for wireless TDMA (time division multiple access) systems equipped with multiple transmit antennas and receive antennas in frequency‐selective fading channels. A novel scheme with space‐time block coding based transmit diversity (STTD) is presented to estimate the multipath channel, coherently demodulate information symbols, and meanwhile suppress radio interference. The proposed scheme is simple to implement and able to mitigate interference of various origins, including intersymbol interference (ISI), cochannel interference (CCI), and others. Numerical examples are presented to illustrate the performance of the proposed estimator and detector in multipath Rayleigh‐fading channels. Copyright © 2002 John Wiley & Sons, Ltd.

Soft capacity analysis of TDMA systems with slow-frequency hopping and multiple-beam smart antennas

Smart antenna is considered as one of the most effective means for enhancing wireless system capacity. When fractional loading is accompanied with slow-frequency hopping (SFH), soft capacity can be realized in time-division multiple access (TDMA) wireless networks. Then, the interference reduction due to smart antennas, power control, and discontinuous transmission can be directly translated into capacity gain. This paper addresses the capacity gain due to multiple-beam (MB) smart antennas in TDMA wireless systems with soft capacity. The system capacity is determined analytically and by simulation. MB smart antennas with practical antenna pattern are used in this study. Perfect power control and discontinuous transmission are assumed in the simulation and the theoretical analysis. A novel call admission control algorithm is proposed to enhance the system capacity without degrading the signal quality. The TDMA system is assumed to be global system for mobile communications (GSM)-like, however, the analysis can be extended and applied to other TDMA systems.

Power control by interference prediction for broadband wireless packet networks

A Kalman-filter method for power control is proposed for broadband, packet-switched time division multiple access wireless networks. By exploiting the temporal correlation of co-channel interference, a Kalman filter is used to predict future interference power. Based on the predicted interference and estimated path gain between the transmitter and receiver, the transmission power is determined to achieve a desired signal-to-interference-plus-noise ratio (SINR). A condition to ensure power stability in the packet-switched environment is established and proven for a special case of the Kalman-filter method. The condition generalizes the existing one for a fixed path-gain matrix, as for circuit-switched networks. Performance results reveal that the Kalman-filter method for power control provides a significant performance improvement. Specifically, when messages consist of ten packets on average, the 90th and 95th percentile of the SINR by the new method are 3.79 dB and 5.46 dB above those when no power control is in use, and lie just 0.96 dB and 1.14 dB below the upper-bound performance of the optimal power control, respectively, in a system with four-sector cells and an interleaved frequency assignment of a reuse factor of 2/8. In addition, the new method performs noticeably better than the delta-modulation method and a simple scheme that uses the last measurement as predicted interference power. In an example of 8-PSK modulation and average message length of 20 packets, the SINR performance gain by the new method improves the network throughput by about 150% and 70%, relative to no power control and the simple scheme, respectively.

A method for multiple channel recovery in TDMA wireless communications systems

A single base repeater failure in time division multiple access (TDMA) wireless systems causes all active calls on this base repeater to be dropped. In order to increase system end-to-end availability, a multiple channel recovery method for TDMA wireless systems is proposed in this paper. By applying the method, when a base repeater fails, the channels of active calls carried by the base repeater are replaced by working channels in the channel pool of the base site. All the active calls continue without the intervention of end users. The method deals not only with the failure and recovery of base repeaters, but also with the channel failure recovery in handoff processes, transient channel failures, and new call setup processes. To predict system availability and performance, hierarchical stochastic reward net models are developed for analyzing channel allocation, base repeater failure/repair, and channel recovery. The results show that the recovery method can nearly eliminate dropped calls when the traffic load is light, and can dramatically reduce dropped calls when the traffic load is normal. The price we pay is a slightly increased blocking probability, nearly transparent to the end users.

Protocol-aided channel equalization in wireless ATM

We study the equalization problem in time division multiple access wireless asynchronous transfer mode (ATM) systems. Aiming at minimizing the overhead associated with equalization, we propose a protocol-aided channel equalization (PACE) approach for wireless ATM. Specifically, the medium access control (MAC) and data link control (DLC) protocols are exploited to provide known ATM cell headers to the receiver at the base station. A blind channel estimation-decision feedback equalizer (BCE-DFE) algorithm is developed for uplink data transmissions. There are two advantages of the BCE-DFE algorithm: the elimination of training symbols for uplink data bursts and the removal of channel estimation error propagation suffered by conventional block equalization schemes. Simulation results show the BCE-DFE has a robust performance for wireless ATM uplink data transmissions over fast time-varying channels.

Performance of an adaptive rate modem using quasi-analytic simulation techniques

The symbol error probability (SEP) of a digital signal processor implemented /spl pi//M M-ary differentially coherent phase-shift keying (MDPSK) modem, using quasi-analytical (QA) simulation techniques, is the subject of this investigation. We study M values of 4, 8, 16, 32, and 64 for use in a fast adaptive data rate mobile radio communication system. The proposed modulation scheme /spl pi//M-MDPSK, is a generalization of /spl pi//4 differentially coherent quadrature phase-shift keying, which is used in the North American time-division multiple-access wireless standard. A QA simulation approach is developed so that real system impairments can be studied without having to resort to lengthy Monte Carlo simulation. In particular, it is found that implementation losses, most notable at M=32 and 64, which result from practical transmit and receive filtering, and symbol timing error, can be largely overcome by using a fixed equalization filter and increased accuracy of symbol timing recovery. We focus on an additive white Gaussian noise channel since, in a fast adaptive rate system, the Doppler spread mobile channel is approximately Gaussian on short time intervals. However, the quasi-analytic technique developed here is directly extendable to a fast Rayleigh fading channel. Specifically, we find that for M=64, the inclusion of a fixed seven-tap zero forcing equalizer at the matched filter output, decreases the SEP degradation at P/sub e/=10/sup -4/ from 7.5 dB down to 0.24 dB. The symbol timing error using a finite-precision interpolator is held to within 1/64 symbol period.

Complex scaled tangent rotations (CSTAR) for fast space-time adaptive equalization of wireless TDMA

A new update algorithm for space-time equalization of wireless time-division multiple access signals is presented. The method is based on a modified QR factorization that reduces the computational complexity of the traditional QR-decomposition based recursive least squares method and maintains numerical stability. Square roots operations are avoided due to the use of an approximately orthogonal transformation, defined complex scaled tangent rotation.