A mobile ad hoc network (MANET) is characterized by multi-hop wireless links in the absence of any cellular infrastructure as well as by frequent host mobility. This paper proposes a SMPQ: Spiral-Multi-Path QoS routing protocol in a MANET, while the MAC sub-layer adopts the CDMA-over-TDMA channel model. This work investigates the bandwidth reservation problem of on-demand QoS routing in a wireless mobile ad-hoc network. The proposed approach increases the ability of a route to identify a robust path, namely a spiral-multi-path, from source host to destination host, in a MANET to satisfy certain bandwidth requirements. Two important contributions of the proposed spiral-multi-path are: (1) the spiral-multi-path strengthens route-robustness and route-stability properties and (2) the spiral-multi-path increases the success rate of finding the QoS route. Performance analysis results demonstrate that our SMPQ protocol outperforms other protocols.

A field trial, within a suburban macro-cell environment, of a space-time (ST) equalizer for TDMA mobile communication systems is described. The ST equalizer was a cascade connection of two array processors for a four-antenna array and a two-branch-metric-combining maximum-likelihood sequence estimation (MLSE) that was designed to obtain full space- and path-diversity gains from first-arrival and one-symbol-delayed signals while suppressing excessively long-delayed inter-symbol interference (ISI). The radio frequency was 3.35 GHz, the transmission rate was 4.096 Mb/s, and the modulation was QPSK. The long-delayed ISI reduction and the space-path diversity effect of the ST equalizer was validated by Eb/N0 vs. bit-error-rate (BER) curves with respect to delay spread and antenna spacing as compared with the case of an array processor alone being used.

The proposed medium access protocol deals especially with the timely-transmission of real-time packets in wireless multimedia networks where users of many types of traffic are present. It works based on Time Division Multiple Access/Time Division Duplex (TDMA/TDD) technique and fixed-length packet switching incorporating two different policies to work differently on either non-congestion or congestion periods. In the policy to deal with congestion periods the concept of urgent packet has been introduced as any packet whose transmission deadline is on the next frame. Hence, during periods of congestion users inform to the Base Station the number and average deadline of the urgent packets in their buffers through requirement messages. According to that information the system is able to distribute its resources in a more efficient way during periods of congestion making the real-time packet loss rate decrease considerably. The simulation results show a very good performance of the method in networks where different types of traffic coexist even under high traffic-load conditions. The results also show a good trade-off characteristic between the real-time access delay and the buffer occupancy of non-real time terminals during congestion periods.

This paper proposes a 2-dimensional linear propagation prediction (LPP) in maximal ratio combining (MRC) transmitter diversity for orthogonal frequency division multiplexing (OFDM) time division multiple access--time division duplex (TDMA/TDD) systems in order to overcome the degradation of the transmission performance due to the fast fading or the TDD duration. In the proposed scheme, the downlink channel condition of each sub-channel is predicted by interpolating the uplink fading fluctuation with both the amplitude and phase, and the predicted downlink channel condition is used for the weighting factor to employ MRC transmitter diversity. Numerical results obtained by the computer simulation show that the proposed 2-dimensional LPP with the second-order Lagrangeis interpolation predicts the downlink channel condition accurately under the fast fading or the long TDD duration. Moreover, in such a condition, the proposed LPP provides far better performance than the conventional 1-dimensional LPP.

In this paper, the co-existence of TDMA and W-CDMA spectrum sharing system (TDMA/W-CDMA overlaid system) with cellular architecture is discussed. In this system, both systems share the same frequency band to improve the spectrum efficiency. Overall rate, bit error ratio (BER) and spectrum efficiency of the system are calculated for the forward link (down-link) in the presence of AWGN channel. Taking into account the path loss and shadow fading loss in this system with cellular architecture, W-CDMA applying interference cancellation (IC) shows a substantial difference in spectrum efficiency, the overlaid system can provide a greater overall rate and higher spectrum efficiency than a single multiple access-based system such as TDMA system or W-CDMA system. The interference cancellation can significantly improve BER of the spectrum overlaid system.

In this paper, we propose a new approach to the adaptive MLSE receiver, which is based on the delay estimation of the paths in the fading channel. The path delays are estimated by using the known training sequence, and based on this estimation the proposed MLSE tracks not the T-spaced equivalent channel but the variations of each path in the frequency-selective channel directly. It will be shown through computer simulations that the proposed MLSE can improve the performance of the conventional MLSE receivers, when the number of paths is small.

Transmitter diversity is a powerful technique to improve the transmission quality of downlink in microcellular mobile communications systems. Under cochannel interference (CCI) at the base station (BS), the transmitter diversity is not necessarily effective, because the desired-plus-interference signal power used as a criterion of downlink branch selection is not always relative to the downlink propagation condition. This paper proposes the theoretical derivation of bit error rate (BER) performance in the transmitter diversity under CCI occurring at BS, as parameters of average SIR at BS, normalized Doppler frequency, and so on. It is confirmed from the correspondence of theoretical results with simulation results that the proposed theoretical approach is applicable to the CCI environments at BS.

In the current digital mobile communication that is used in the micro cellular system, a Self-Organized Dynamic Channel Assignment (DCA) Method has been proposed to use frequencies effectively. However, its characteristics and operational matters have not been reported yet. This paper takes up the TDMA/TDD system used in the current PHS system and also evaluates the characteristics and operational matters of this method through the actual operational tests. In addition, this paper aims to propose a new DCA method in order to speed up the Channel Segregation and evaluates its effects through the actual operational tests.

In software-based wireless multimedia communications systems, each mobile terminal will be able to select its best-suited transmission format according to its quality of service (QoS) and channel condition. In this paper, we focus attention on "access scheme selectability" in such a software-based system, and discuss the traffic performance improvement due to adaptive access scheme selection. Assuming a software-based TDMA/CDMA system where time division multiple access (TDMA) and direct sequence code division multiple access (DS-CDMA) schemes are flexibly selectable, we evaluate the traffic performance in terms of average delay with a typical multimedia service model to be supported in future wireless communications systems. In the TDMA/CDMA system, how to determine an appropriate access scheme for a user is a key issue. Therefore, we discuss the selection algorithm for efficiently supporting heterogeneous multimedia services. Our computer simulation results show that the software-based system with a simple access scheme selection algorithm can significantly improve the traffic performance as compared with conventional hardware-based systems.

This paper describes the results of a series of laboratory experiments for performance evaluations of our proposed Maximum Likelihood Sequence Estimation (MLSE) based interference canceller, the Interference Canceling Equalizer (ICE), which can cancel both co-channel interference (CCI) and inter-symbol interference (ISI). To verify the feasibility of ICE for the Japanese cellular communications system, a standard of which has been released under the name of Personal Digital Cellular (PDC) system, a prototype system was constructed using 27 TI TMS320C40 Digital Signal Processor (DSP) chips. The ICE prototype works in real-time on the PDC air interface, major specifications of which are π/4 QDPSK 21 k symbols/s 3-channel time-division multiple-access (TDMA). Two-branch diversity reception is used to enhance the signal detection performance of ICE. In the experiments, BER performances were evaluated using the prototype system. Under a single-path Rayleigh fading and a single CCI condition, the ICE receiver attains the BER of less than 310-2 with the negative values of the average CIR: for fD = 5 Hz and 40 Hz, the average CIR more than -20 dB and -10 dB, respectively. Under a double-path Rayleigh fading and a single CCI condition, the ICE receiver attains the BER of less than 1.510-2 with the negative values of the average CIR: for fD = 5 Hz and 40 Hz, the average CIR more than -20 dB and -10 dB, respectively. The laboratory test results suggest that the ICE receiver has potential for system capacity enhancement.

Designing control and robotic systems as autonomous decentralized systems introduces a new degree of flexibility in the manufacturing and in the application of such systems. This flexibility is required for the systems to work in environments that are not totally predictable and that can change dynamically. In this paper, we present a new concept for real-time communication that supports this flexibility while still preserving real-time guarantees for hard real-time communication. The concept is designed to work on multiple-access busses. In particular, we consider its application on wireless local area networks and field-busses. The concept addresses requirements of hard-real time, soft real-time and non real-time communication. For this, we extend the TDMA (time- division multiple-access) approach for time-triggered hard-real time communication by the concept of shared channels that support event-triggered communication and coexist with hard real-time channels. A first implementation of concept has been carried out in the context of the CAN-bus.

In this paper, we propose a polling-based scheduling strategy for multiple access control in wireless ATM networks (POSTMAN). A pure centrally controlled polling scheme is adopted in our protocol, therefore no contention channel is needed. The POSTMAN protocol assumes a TDMA/TDD frame format, by which wireless bandwidth is allocated flexibly both among multiple mobile terminals and between downlink and uplink channels. When polling the uplink traffic, the POSTMAN needs no priori traffic model to predict the cell arrivals. Instead, a token queue and an ABR buffer status table are used in the base station. Simulation results show that the POSTMAN protocol is robust in most cases and can work steadily under very high network load conditions.

Minimizing the guard time, Tguard, in the TCM-TDMA PDS scheme is essential in maximizing TCM transmission efficiency. As a replacement for the commonly adopted worst-case approach to TCM-TDMA PDS system estimation, this paper proposes a statistical approach. The level distributions of losses and n-th order Fresnel reflections are determined from published measurements. The proposed approach estimates the reflection of the optical access network.

A novel combinatorial optimization algorithm called "Gradual neural network (GNN)" is presented for NP-complete broadcast scheduling problems in packet radio (PR) networks. A PR network provides data communications services to a set of geographically distributed nodes through a common radio channel. A time division multiple access (TDMA) protocol is adopted for conflict-free communications, where packets are transmitted in repetition of fixed-length time-slots called a TDMA cycle. Given a PR network, the goal of GNN is to find a TDMA cycle with the minimum delay time for each node to broadcast packets. GNN for the N-node-M-slot TDMA cycle problem consists of a neural network with N M binary neurons and a gradual expansion scheme. The neural network not only satisfies the constraints but also maximizes transmissions by two energy functions, whereas the gradual expansion scheme minimizes the cycle length by gradually expanding the size of the neural network. The performance is evaluated through extensive simulations in benchmark instances and in geometric graph instances with up to 1000 vertices, where GNN always finds better TDMA cycles than existing algorithms. The result in this paper supports the credibility of our GNN algorithm for a class of combinatorial optimization problems.

For two-tier cellular network design, resource management between tiers is an important issue to be studied. In this paper, in order to use the network resources preciously, we considered sharing of the available spectrum between the tiers. We evaluate this sharing for two network architectures. In the first architecture, called System I, DS-CDMA is deployed in both tiers. In the second architecture, called System II, TDMA is deployed for users in the microcell tier and CDMA for macrocell users. Using analytically evaluated intercell interference for a two-tier cellular system, we will show the performance and the allowable system capacity for the above systems.

MTDMA (Multimedia, Multimode TDMA) system has been developed for the 3rd generation mobile communications. An adaptive modulation technique is employed, which select 16 QAM or QPSK modulations fit for the O (Indoor Office)/P (Outdoor to Indoor and Pedestrian) communication environments. The maximum user rate of 4 Mbps is realized. Basic specification is described for O, P and V environments.

This paper gives laboratory as well as the results of field experiment and describes the implementation of a system developed to evaluate and demonstrate multimedia multimode time division multiple access (MTDMA). The equipment has been developed with the radio transmission technology for future public land mobile telecommunication systems (FPLMTS/IMT-2000) in mind. To meet FPLMTS/IMT-2000 requirements the system employs the following techniques: a hybrid multiplex modulation system consisting of quadrature phase shift keying (QPSK) and 16-ary quadrature amplitude modulation (16QAM), a high data transmission bit rate of 2 Mbit/sec for QPSK, 4 Mbit/sec for 16QAM, and diversity combining and adaptive equalization technique. For the diversity adaptive equalization technique, we used a decision feedback equalizer (DFE) consisting of one feedback (FB) transversal filter and two feed-forward transversal (FF) filters. The output signals from two branches of space diversity reception antennas are then fed to the two FF filters of the DFE. For middle-speed mobile radio communication for a micro-cellular pedestrian environment, a QPSK modulation system is selected to obtain wide coverage, while for a pico-cellular indoor office environment, the delay spread is small, and a 16QAM modulation system is selected to achieve a high bit rate. The results given here of laboratory and field experiments show the technical feasibility of MTDMA for future public land mobile telecommunication systems.

The applications of adaptive arrays based on the digital beam forming technique are receiving wide attention. However, the adaptive control algorithm of the array antennas under TDMA systems is not well considered even though it requires particular consideration due to its intermittent bursts. In this paper, first, we propose a novel DOA (Direction of Arrival) estimation method which is suitable for TDMA bursts. Second, the HA (Howells-Applebaum) adaptive array based on the proposed DOA estimation method will be constructed for the terminals in the mobile communication systems using non-geostationary satellites . Then the performance of the DOA estimation method and the HA adaptive array will be examined through computer simulations and experiments.

This paper proposes a new MAC protocol and physical channel control schemes for TDMA-TDD multi-slot packet channel. The goal of this study is to support both circuit-switched and packet-switched communications on the same resources and to enable high-speed packet transmission using a multi-slot packet channel. In the proposed channel control schemes, three points are taken into account; 1) effective sharing of time slots and frequencies with minimum impact on circuit communications, 2) compatibility with the existing access protocol and equipment, and 3) dynamic allocation of uplink and downlink slots. As for the MAC protocol, we adopt BRS (Block Reservation Scheme) and adaptive access control scheme to the proposed MAC protocol. In addition, to overcome the inherent disadvantage of TDD channels, packet scheduling and access randomizing control are newly proposed in this paper. The results of throughput and delay evaluations confirm that downlink capacity can be drastically enhanced by the dynamic allocation of uplink and downlink slots while corruption under heavy traffic loads is prevented by applying the adaptive traffic load control scheme.

It is indispensable to establish a multi-access protocol and resource management technique that can assure transmission quality and efficiently utilize the radio frequency spectrum for ATM-based wireless access systems. This paper proposes dynamic time-slot assignment schemes for the forward link from a user to a central station (CS): (1) the centralized assignment and release scheme (CAR), and (2) the centralized-assignment and autonomous-release scheme (CAAR). In the proposed schemes, a central station dynamically assigns time-slots based on traffic information obtained by monitoring the input traffic in each radio module (RM). In addition, forward protection is used to prevent false-release of assigned time-slots. Performance evaluations have been carried out by analysis as well as computer simulations. They show that the proposed schemes achieve good performance in delay, link stability, and utilization efficiency of radio resources with an optimized number of forward protection steps.