TDMA System Research Articles

A Jain's Index Perspective on α-Fairness Resource Allocation over Slow Fading Channels

In this letter, by focusing on α-fairness resource allocation in single channel TDMA system with slow Rayleigh fading, we study the impacts of α on the system efficiency and Jain's index which is widely used as a fairness measure. Also, we prove that increasing α results in higher efficiency but lower Jain's index and reveal the role of α in controlling the tradeoff between efficiency and fairness. Furthermore, an algorithm is proposed to find the optimal α under a system efficiency constraint or a Jain's index constraint with fast convergence and low complexity.

Dynamic Cooperative Retransmission Scheme for TDMA Systems

In this letter, we propose and analyze a dynamic cooperative retransmission scheme for TDMA systems in multi-hop networks. Our scheme cooperatively retransmits a failed packet during a neighbor node's idle slot, which is selected using a simple mechanism. If an idle slot is not available, cooperative retransmission is attempted during the source node's time slot. The throughput of TDMA can be significantly improved by cooperative retransmission. We formulate an analytical model for the proposed scheme that can be implemented over Rayleigh fading channels. The results showed that the throughput of TDMA systems was improved significantly if a sufficient number of idle slots were available for cooperative retransmission, although an overhead was introduced.

Cluster-Based Control Channel Allocation in Opportunistic Cognitive Radio Networks

Cognitive radio networks (CRNs) involve extensive exchange of control messages, which are used to coordinate critical network functions such as distributed spectrum sensing, medium access, and routing, to name a few. Typically, control messages are broadcasted on a preassigned common control channel, which can be realized as a separate frequency band in multichannel systems, a given time slot in TDMA systems, or a frequency hopping sequence (or CDMA code) in spread spectrum systems. However, a static control channel allocation is contrary to the opportunistic access paradigm. In this paper, we address the problem of dynamically assigning the control channel in CRNs based on time- and space-varying spectrum opportunities. We propose a cluster-based architecture that allocates different channels for control at various clusters in the network. The clustering problem is formulated as a bipartite graph problem, for which we develop a class of algorithms that provide different tradeoffs between two conflicting factors: number of common channels in a cluster and the cluster size. Clusters are guaranteed to have a desirable number of common channels for control, which facilitates for graceful channel migration when primary radio (PR) activity is detected, without the need for frequent reclustering. We perform extensive simulations that verify the agility of our algorithms in adapting to spatial-temporal variations in spectrum availability.

위성통신을 위한 강인한 TDMA Frame 구조 및 초기동기 기법

A TDMA system in satellite communication has been utilized. Especially DVB-S2 was standardized and now operated in satellite broadcasting system. In this paper, we propose a TDMA frame structure appropriate for special purpose which has the good reliablilty in a poor RF environment even if frequency efficiency is decreased. TDMA frame duration is 12 seconds which is long duration in comparison with general TDMA system with several ms. Designing the frame structure, time and frequency shift in single frame duration are considered. Simulation results show that the proposed frame structure and synchronization method has robust synchronization performance when the terminal is even in low SNR as well as 25 ㎑ frequency offsets.

Area-efficient programmable arbiter for inter-layer communications in 3-D network-on-chip

Abstract The Network-on-Chip (NoC) is an emerging communication technique for System-on-Chip (SoC) communications. The NoC uses multiple processors, usually targeted for embedded applications and other applications [3, 13]. Performance of the bus is degraded by the increasing number of processing elements and transaction oriented model [13]. This has attracted much attention for applying wireless network protocols as CDMA, TDMA, and dTDMA in SoC. The TDMA systems use a fixed number of timeslots. This protocol wastes bandwidth when some timeslots are allocated but not used. The dynamic TDMA (dTDMA) bus arbiter dynamically grows and shrinks the number of timeslots to match the number of active transmitters [14]. In this paper, we present a design of area-efficient switch for inter-layer communications in 3-D NoC. The arbitration logic in the switch is based on a programmable priority encoder. A 640-bit message with uniform random destination data pattern was injected per IP per machine clock cycle. We have obtained the maximum clock frequency of 2.09 GHz for 96(4 × 8 × 3) IP cores connected in a mesh topology. The presented architecture demonstrates their superior functionality in terms of speed, latency, area, and power consumption as compared with the existing implementation [14]. The maximum power consumption of the proposed area-efficient programmable arbiter is 0.625 mW. The design is synthesized using 180nm TSMC Technology.

High-speed dynamic TDMA arbiter for inter-layer communications in 3-D network-on-chip

The conventional two-dimensional 2-D integrated circuit IC has limited scope for floor planning and therefore limits the performance improvements resulting from the Network-on-Chip NoC paradigm. The arrangement of 3-D also offers opportunities for new circuit architecture based on the geometric capacity that provide greater numbers of interconnections among multi-layer active circuits. The emerging 3-D VLSI Integration and process technologies allow the new design opportunities in 3-D NoC. The 3-D NoC can reduce significant amount of wire length for local and global interconnects. The role of bus and arbitration logic is equally important in the design of NoC. The performance of the traditional bus is degraded by the increasing number of processing elements and transaction oriented model [On-Chip Communication Architectures, Morgan Kaufmann, 2008]. This has attracted much attention for applying wireless network protocols as CDMA, TDMA, dTDMA, etc. in SoC. The TDMA systems use a fixed number of timeslot. This protocol wastes bandwidth when some timeslots are allocated but not used. The dynamic TDMA dTDMA bus arbiter dynamically grows and shrinks the number of timeslots to match the number of active transmitters [in: VLSI Design, 2006. Held jointly with 5th International Conference on Embedded Systems and Design, 19th International Conference on, January 2006, p. 8]. In this paper, we present a design of high-speed switch and layer arbiter for inter-layer communications in 3-D Network-on-Chip. We have developed a Register Transfer Logic RTL level simulation model to evaluate the performance of proposed arbiter. A 640-bit message with uniform random destination data pattern was injected per IP per machine clock cycle. The worst case latency for the proposed design is 35 clock cycles. The presented architecture demonstrates their superior functionality in terms of speed and latency compared with existing implementation. The design is synthesized using 0.18 micron TSMC Technology [Taiwan Semiconductor Manufacturing Company, Ltd, 2011].

Optimal power and subcarriers allocation in downlink OFDMA system with imperfect channel knowledge

Most of existing work on resource allocation in TDMA and OFDMA systems assumes the availability of perfect channel state information (CSI) at the transmitter, which is rarely possible due to feedback delay and channel estimation error. In this paper, we study the effect of feedback delay and channel estimation error on margin adaptive resource allocation in a downlink OFDMA system. By using convex optimization framework, we find an optimal solution to the problem. First, we study the individual effect of feedback delay and channel estimation error on resource allocation by considering them exclusively. Then, we consider the simultaneous presence of feedback delay and channel estimation error and study their combined effect on resource allocation. We derive an explicit close form expression for the users’ transmit power and propose an algorithm for power and subcarriers allocation for each of these three scenarios. The algorithms have polynomial complexities and solve the problem with zero optimality gaps. Simulation results show that the system performance is very sensitive to feedback delay and is affected significantly by imperfect channel estimation. Our proposed algorithms highly improve the system performance in the availability of only imperfect CSI at the transmitter.

On channel-discontinuity-constraint routing in wireless networks

Multi-channel wireless networks are increasingly deployed as infrastructure networks, e.g. in metro areas. Network nodes frequently employ directional antennas to improve spatial throughput. In such networks, between two nodes, it is of interest to compute a path with a channel assignment for the links such that the path and link bandwidths are the same. This is achieved when any two consecutive links are assigned different channels, termed as “Channel-Discontinuity-Constraint” (CDC). CDC-paths are also useful in TDMA systems, where, preferably, consecutive links are assigned different time-slots.In the first part of this paper, we develop a t-spanner for CDC-paths using spatial properties; a sub-network containing O(n/θ) links, for any θ>0, such that CDC-paths increase in cost by at most a factor t= (1−2 sin(θ/2))−2. We propose a novel distributed algorithm to compute the spanner using an expected number of O(nlogn) fixed-size messages.In the second part, we present a distributed algorithm to find minimum-cost CDC-paths between two nodes using O(n2) fixed-size messages, by developing an extension of Edmonds’ algorithm for minimum-cost perfect matching. In a centralized implementation, our algorithm runs in O(n2) time improving the previous best algorithm which requires O(n3) running time. Moreover, this running time improves to O(n/θ) when used in conjunction with the spanner developed.

Interference Reduction in Overlaid WCDMA and TDMA Systems

In this paper, the performance of WCDMA uplink system for UMTS mobile communications is evaluated. Also, the possibility of increasing mobile communication cell capacity through merging WCDMA and TDMA systems in one cell is investigated. An interference canceller is proposed to reduce, or even completely cancel, the interference between WCDMA and TDMA, hence enabling them to work together. This results in a considerable increase in the cell capacity. The coexistence of WCDMA and TDMA systems in one cell is proven to be possible via computer simulations.

LokVaani

In this work, we consider the goal of enabling effective voice communication in a TDMA, multi-hop mesh network, using low cost and low power platforms. We consider two primary usage scenarios: (1) enabling a local voice communication within a village-like setting, in developing regions (2) supporting an on-site local communication among a team of users e.g. during emergency response systems. While there is plentiful literature on the use of TDMA for multi-hop wireless mesh networks, a practical multi-hop TDMA system remains elusive. Our contributions in this regard are three-fold. (1) We demonstrate the working of an 802.15.4-based low-cost, low-power, local communication system (referred as Lo3) using custom made handsets and off-the-shelf platforms. (2) We show the practicability of LiT: a full-fledged TDMA-based multi-hop, multi-channel MAC protocol for real-time applications; especially on resource constrained platforms, (3) We present implementation-based evaluations results of LiT and show that our protocol achieves practical synchronization, and robust operation in the face of wireless packet errors. As the part of the demo, we showcase LokVaani: an interactive voice application for local communication with the help of Lo3 prototype.

Esquemas de ordenamiento en sistemas celulares sobrepuestos CDMA

The CDMA overlay concept, has been proposed as one alternative to take advantage of the band width available in narrowband systems. In fact, the basic idea of the CDMA overlay is to allow to wideband CDMA wave forms, to share a common spectrum with narrowband conventional wave forms. In this work, we have focused in the analysis of the performance of the forward link of the CDMA and TDMA systems when they are over laid. In our model, in order to limit the interference into the CDMA layer caused by the TDMA system, the use of notch filters has been considered. However, one draw back of the filters is that it rejects only one part of the interference generated by the TDMA system. Therefore, we have proposed two new ideas of reduction of the interference which can not be eliminated by filters; ordered hunt and real location of the slots. Finally, we present an analytical evaluation of the forward link capacity of the systems involved in the over laid process, due to this is the limiting link and as a function of the outage probabilities. Practical considerations such as power requirements, power control, handoff, the offered load for different services and scenarios are also addressed.

Rate regulated TDMA system for cochannel interference limited wireless ad hoc networks

The time slotted system with rate regulation, which adapts the transmission rate to the interference for each time slot, is proposed to enhance the throughput while meeting the SINR requirement for cochannel interference limited wireless ad hoc networks. We show that the throughput of the rate regulated TDMA system is larger than that of the rate regulated TDMA/CDMA system. Furthermore, we also propose a scheduling algorithm to maximize the total throughput of the rate regulated TDMA system.

Use of Tree Traversal Algorithms for Chain Formation in the PEGASIS Data Gathering Protocol for Wireless Sensor Networks

The high-level contribution of this paper is to illustrate the effectiveness of using graph theory tree traversal algorithms (pre-order, in-order and post-order traversals) to generate the chain of sensor nodes in the classical Power Efficient-Gathering in Sensor Information Systems (PEGASIS) data aggregation protocol for wireless sensor networks. We first construct an undirected minimum-weight spanning tree (ud-MST) on a complete sensor network graph, wherein the weight of each edge is the Euclidean distance between the constituent nodes of the edge. A Breadth-First-Search of the ud-MST, starting with the node located closest to the center of the network, is now conducted to iteratively construct a rooted directed minimum-weight spanning tree (rd-MST). The three tree traversal algorithms are then executed on the rd-MST and the node sequence resulting from each of the traversals is used as the chain of nodes for the PEGASIS protocol. Simulation studies on PEGASIS conducted for both TDMA and CDMA systems illustrate that using the chain of nodes generated from the tree traversal algorithms, the node lifetime can improve as large as by 19%-30% and at the same time, the energy loss per node can be 19%-35% lower than that obtained with the currently used distance-based greedy heuristic.

Scheduling schemes for multimedia service in wireless OFDM systems

Scheduling schemes play a key role in the system performance of broadband wireless systems such as WLANs/WMANs. Maximal SNR and round robin are two conventional scheduling strategies that emphasize efficiency and fairness, respectively. The proportional fair scheme provides a trade-off between efficiency and fairness, and has been well studied in TDMA and CDMA systems. In this article we extended the PF scheduling scheme to OFDM-based BWSs (OPF). In addition, we propose three variations: adaptive OPF (AOPF), multimedia AOPF (MAOPF), and normalized MAOPF (NMAOPF) in order to meet the QoS requirements for multirate services in multimedia systems. The adaptive modulation and coding schemes in time varying and frequency selective fading are considered. The system performances of the algorithms are compared in terms of efficiency (throughput and mean packet delay) and fairness (user satisfaction rate and average user rate). Joint physical and media access control layer simulation results show that AOPF and MAOPF can improve throughput at the cost of fairness, and NMAOPF can provide the highest throughput without losing fairness.

A method for determining thermophysical properties of organic material in aqueous solutions: Succinic acid

A method for determining evaporation rates and thermodynamic properties of aqueous solution droplets is introduced. The method combines evaporation rate measurements using modified TDMA technique with data evaluation using an accurate evaporation model. The first set of data has been collected and evaluated for succinic acid aqueous solution droplets. Evaporation rates of succinic acid solution droplets have been measured using a TDMA system at controlled relative humidity (65%) and temperature (298 K). A temperature-dependent expression for the saturation vapour pressure of pure liquid phase succinic acid at atmospheric temperatures has been derived by analysing the evaporation rate data with a numerical model. The obtained saturation vapour pressure of liquid phase succinic acid is ln( p) = 118.41 − 16204.8/ T − 12.452ln( T). The vapour pressure is in unit of Pascal and the temperature in Kelvin. A linear expression for the enthalpy of vaporization for liquid state succinic acid is also presented. According to the results presented in the following, a literature expression for the vapour pressure of liquid phase succinic acid defined for temperatures higher than 461 K [Yaws, C.L., 2003. Yaws' Handbook of Thermodynamic and Physical Properties of Chemical Compounds, Knovel] can be extrapolated to atmospheric temperatures with very good accuracy. The results also suggest that at 298 K the mass accommodation coefficient of succinic acid is unity or very close to unity.

Microscopic spectrum control technique using carrier interferometry for one-cell reuse single carrier TDMA system

Proposed is a microscopic spectrum control technique using carrier interferometry for adaptive modulation based one-cell reuse single carrier TDMA systems. To enhance interference immunity, adaptive spectrum selection according to the received SINR is introduced. Computer simulation confirms the proposed scheme is effective in improvement of interference immunity.

System Throughput Analysis of Rate Adaptive TDMA System Supporting Two Class Services

In this paper, an adaptive transmission scheme is proposed to improve the spectral efficiency of TDMA systems. Services accommodated in such systems are classified as QoS services and BE services. Unlike conventional adaptive TDMA systems where the time slot duration is fixed for each user, our proposed system employs transmission slots with adaptive duration. For QoS services, rate adaptive modulation is adopted to make use of the instantaneous channel conditions of individual user. For BE services, a media access control strategy (MAC) that takes the instantaneous transmission conditions of all physical links of all BE services into consideration is employed. A tramework to study the proposed system in terms of the average packet loss and the average system throughput is presented. The maximum nuumber of QoS services that can be supported in the system while a predefined requirement on the average packet loss is still satisfied is investigated. A comparison study shows that our proposed scheme has higher system throughput over both conventional fixed and adaptive TDMA systems.

A Feedback Type Adaptive Array Antenna with One Bit Feedback Information and Adaptive Update Size in FDD System

The purpose of this paper is to improve a feedback-type adaptive array antenna (AAA) with feedback information quantized by one bit which was presented recently on TDMA system by an author of this paper. The improvement is made by using adaptive, instead of constant, update size of adaptive antenna weights control. Computer simulation results show that the performance of this system is improved to be almost equivalent to the performance of a system without quantization of the feedback information for wide range of fading speed. The results include the effect of control delay time and the maximum Doppler frequency under flat fading and frequency-selective fading.

Impact of tradeoff between blocking and interference on TDMA cell capacity planning

Cell capacity planning is a key phase of the expansion of cellular networks. The growth of communications demand requires improving the capacity of the networks regularly. However, cell capacity planning is difficult to achieve while it must take into account two conflicting objectives: minimising the blocking rate and reducing the interference. In TDMA systems, current literature offers few studies dealing simultaneously with both criteria. In this paper, we propose a bicriteria model for TDMA cell capacity planning as answer to a flexible management of the tradeoff between blocking and interference phenomena. While cell capacity dimensioning requires the offered traffic load on each station, we also present a module for offered traffic computation where user retrials and redials are considered. At the end, we carry out tests on two real world datasets with different network architectures and traffic loads in order to assess the efficiency of the approach.

Fast and stable acquisition by utilizing multi-component code under very low C/N conditions: Application to acquisition in TDMA satellite communication systems

The method of frame synchronization in which the acquisition time is drastically reduced by using multi-component code is well known. There is a danger in this method, however, that large acquisition delays may occur in a low C/N environment due to errors of the partial correlation values. The purpose of this paper is to apply a multi-component code to acquisition in an effort to improve the performance of TDMA systems. The operation of the proposed acquisition method and the acquisition time performance in a low C/N environment are evaluated by experiment, theoretical analysis, and computer simulation and guidelines for acquisition system design to achieve fast and stable operation are proposed. The S/N value at the correlator output required for realizing the desired performance is determined. It is also shown here that performance can be improved greatly by providing a correlation detector with hysteresis. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(5): 50–66, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20157