ACTS TDMA network control architecture

Space division multiple access (SDMA) has attracted considerable attention as a means for increasing the capacity in cellular communications. For the service provider the smart antenna could provide a much-needed device to boost capacity by decreasing the effect of interference and thereby increase user capacity in congested areas. However, questions arise as to the best trade-offs for implementing SDMA. In this paper, we develop a tool for evaluating the use of SDMA in time division multiple access (TDMA) systems. The approach is based on evaluating the outage probability due to cochannel interference in fading at the base station of a TDMA system assuming an ideal beamformer model. The statistical model developed takes into account both spatial and temporal components of the interference signal. We use the model to then bound the performance improvement. The performance improvement is with respect to a base station employing an omnidirectional antenna. The bounds for the performance are based on looking at a range of smart antenna complexity. In addition, TDMA systems with different levels of acceptable time coincidence between the desired mobile's signal and interfering mobiles' signals are considered. The simulation results indicate a performance improvement spread from 8 to 36 dB.

Two candidates for high-capacity cellular systems are simulated and analyzed, one code-division multiple access (CDMA) and one time-division multiple access (TDMA) system. Simulations of the CDMA example indicate a high sensitivity to variations in certain system parameters. The TDMA example is a GSM system using random frequency hopping and operating without frequency planning. The simulations show that the TDMA system has at least the same capacity as the CDMA candidate. Soft capacity, efficient use of voice activity, and diversity are features available in both systems. >

Application of Multirate Filter Bank to the Co-Existence Problem of DS-CDMA and TDMA Systems

To implement a one-cell reuse time division multiple access (TDMA) system using orthogonal frequency division multiplexing-based adaptive modulation scheme (OFDM AMS) and multilevel transmit power control (MTPC), co-channel interference [intercell interference (ICI)] from adjacent cells that varies dynamically on the frequency axis must be fed back very accurately to the transmitting station. Therefore, in this paper, we propose an ICI feedback technology in one-cell reuse TDMA with OFDM AMS/MTPC. First, the interference power of each subchannel is estimated by calculating the vector error which is the difference between the reference symbol on the receiving side and the received symbol. Next, instead of a digital signal method capable of expanding the amount of information, analog quadrature amplitude modulation (QAM) is adopted in order to feed back the errors with high accuracy. In addition, code division multiplexing (CDM) is adopted in order to improve the robustness to multipaths. Furthermore, to reduce the amount of feedback information, we adopt a method where the estimated interference noise power is formed into blocks by multiple adjacent subcarriers, and only the average of the block is set as the notification target, and interference power information less than some constant value is not notified. The evaluation results of the characteristics of the proposed method by a computer simulation verified that the interference noise power can be estimated very accurately and can accurately notify by using a notification frame with optimized power distribution. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(7): 11–23, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20281

Chapter 6 - Digital & Digital/Analogue Communications Systems

This paper discusses the problem of coexistence of DS-CDMA (direct sequence code division multiplex access) and TDMA (time division multiple access) systems where their signals are transmitted in the same frequency band. The DS-CDMA signal is robust against narrowband interference, but there is a limit to its immunity against interference. This paper proposes, from such a viewpoint, a method using a complex multirate filter bank, as a way to reject TDMA signals, which act as narrowband interference to the DS-CDMA signal, in the coexistence system. By the proposed method, a notch filter can be composed with an arbitrary frequency resolution at an arbitrary frequency, by constructing the complex version of the conventional multirate filter bank. It is shown that, by eliminating the TDMA signal by the proposed method, the bit error rate of the DS-CDMA signal is improved, indicating that the proposed system is useful in the coexistence problem. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(5): 34–41, 1999

We investigate the interuser interference in cellular code—division multiple access (CDMA) and timedivision multiple access (TDMA) systems and compare the two multiple access techniques at different levels of user density per cell. The study includes the interference both on the downstream channel (from base station to users) and on the upstream channel (from users to base station). The purpose is to compare the two multiple access techniques when the total bandwidth occupancy and the maximum number of users per cell are the same. The results indicate that on a nondispersive radio channel with a path loss that is proportional to the fourth power of the distance, the interuser interference is approximately 10 dB higher in CDMA. The implication of this result, which holds for both the downstream and the upstream channels, is that for the same total bandwidth and number of users per cell, TDMA gives substantially superior bit error rate (BER) performance. This is confirmed by our numerical results evaluated for both additive white Gaussian noise (AWGN) channels and memoryless flat Rayleigh fading channels. Alternatively, CDMA needs approximately 10 times more bandwidth to achieve the same signal—to—interference (S/I) ratio, a result which may seem surprising, because the fact that CDMA employs a frequency reuse factor of 1 is often given as an evidence that this technique can support a higher number of users than TDMA in a given geographic area and frequency bandwidth.

We estimate capacities of code-division multiple access (CDMA) and time-division multiple access (TDMA) systems when applied to an air-to-ground/ground-to-air (AG/GA) environment. Our analysis is based upon a regular cellular arrangement of ground stations (bases), as in the land-mobile environment, and uses waveforms based upon current cellular standards. Two of the most crucial parameters for capacity estimation, unique for the air-to-ground environment, are the outside-cell interference factor for CDMA and the frequency re-use factor for TDMA. These are computed, using a quasi-two-dimensional (2D) analysis, for average and worst-case conditions, taking into account radio propagation effects at VHF/UHF. We also investigate variations from conventional system operational modes: half-duplex for TDMA, and 1/3 frequency re-use for CDMA. We provide capacity estimates vs. cell size, and show that (as in the cellular case), capacity depends upon the many available system parameters, in addition to cell size.

In a network application, channel coding alone is not sufficient to reliably transmit a message of finite length K from a source to one or more destinations as in, e.g., file transfer. To ensure that no data is lost, it must be combined with rateless erasure correcting schemes on a higher layer, such as a time-division multiple access (TDMA) system paired with automatic repeat request (ARQ) or random linear network coding (RLNC). We consider binary channel coding on a binary symmetric channel (BSC) and q-ary RLNC for erasure correction in a star network, where Y sources send messages to each other with the help of a central relay. In this scenario RLNC has been shown to have a throughput advantage over TDMA schemes as K→∞ and q→∞. In this paper we focus on finite block lengths and compare the expected throughputs of RLNC and TDMA. For a total message length of K bits, which can be subdivided into blocks of smaller size prior to channel coding, we obtain the channel code rate and the number of blocks that maximize the expected throughput of both RLNC and TDMA, and we find that TDMA is more throughput-efficient for small message lengths K and small q.

We estimate capacities of code-division multiple access (CDMA) and time-division multiple access (TDMA) systems when applied to an air-to-ground/ground-to-air (AG/GA) environment. Our analysis is based upon a regular cellular arrangement of ground stations (bases), as in the land-mobile environment, and uses waveforms based upon current cellular standards. Two of the most crucial parameters for capacity estimation, unique for the air-to-ground environment, are the outside-cell interference factor for CDMA and the frequency re-use factor for TDMA. These are computed, using a quasi-two-dimensional (2D) analysis, for average and worst-case conditions, taking into account radio propagation effects at VHF/UHF. We also investigate variations from conventional system operational modes: half-duplex for TDMA, and 1/3 frequency re-use for CDMA. We provide capacity estimates vs. cell size, and show that (as in the cellular case), capacity depends upon the many available system parameters, in addition to cell size.

Due to their variability Fibre Bragg Grating (FBG) sensors are introduced in a growing number of applications. Furthermore using their spectral selectivity and adjustable reflectivity these sensors are predestined for serial networking, whereby presently in most cases the addressing is realised by time division multiple access (TDMA) or wavelength division multiple access (WDMA). But these technologies have big disadvantages regarding the effective use of the prevailing resources time and wavelength, respectively. In this paper a new scheme capable of addressing a large number of FBGs in a single serial network is proposed and compared to TDMA and WDMA. Using all optical sequence inversion keyed (SIK) direct sequence (DS) code division multiple access (CDMA) it overcomes the restrictions handling the resources time and wavelength without loosing accuracy. A simulation with 20 FBGs in a spectral range of 2nm shows the abilities of this system, which can be build up with nearly the same components as TDMA systems.

This paper analyzes the characteristics of time division multiple access (TDMA) scheme to improve the performance of data transmissions in wireless networks. After analyzing these characteristics, we design an efficient medium access control (MAC) mechanism based on our analysis. Because of the variable characteristics of TDMA we analyzed, we could get a time slot period to achieve the system throughput more optimal. Our proposed protocol is based on our analysis and schedule with a carefully computation. The slot(s) can be divided into several minislots as the contention interval which is used by subscribers to transmit the control packets to base station. We conclude with an approximate optimal throughput through our MAC mechanism.

We investigate the multiuser interference on the downlink channel (from base station to users) in cellular code-division multiple access (CDMA) and time-division multiple access (TDMA) systems. The results indicate that for the same total bandwidth occupancy and maximum number of users per cell, multiuser interference is approximately 10 dB higher in CDMA in fully-loaded cells. The implication of these results is that for the same total bandwidth and number of users per cell, TDMA gives significantly superior bit error rate (BER) performance, as confirmed by our numerical results on additive white Gaussian noise (AWGN) channels as well as on flat Rayleigh fading channels. Alternatively, CDMA needs approximately 10 times more bandwidth than TDMA to achieve the same signal-to-interference ratio (SIR) and bit error rate (BER) performance in fully loaded cells.

A high capacity time division multiple access (TDMA) cellular system that employs a pilot-symbol aided 16 quadrature amplitude modulation (QAM), block coding, and cyclical slow frequency hopping is presented. The QAM scheme increases the information bit rate per bandwidth. The combination of frequency hopping and coding offers immunity against interference and contributes to increasing the frequency reuse factor. The simulation results show that the proposed system can achieve a channel capacity comparable to that of a code division multiple access (CDMA) system.

A computer simulation tool for evaluating the speech traffic handling capability of digital cordless telecommunications systems has been developed. The focus of the paper lies on the teletraffic engineering problems posed by time division multiple access (TDMA) systems operating with time division duplex (TDD) on one radio transceiver in radio environments. The impacts of fixed station separation, fixed station capacity, spatial traffic variability, dynamic channel assignment, microdiversity, and propagation model on the system capacity are investigated. The simulator serves as an invaluable tool for conducting sensitivity studies and its outputs provide useful insights on traffic performance of digital cordless systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>