A dynamic channel assignment algorithm for a hybrid TDMA/CDMA-TDD interface using the novel TS-opposing technique

We propose a framework for network-assisted radio resource management in wireless data networks. This type of radio resource management techniques offer implementation and capacity benefits compared to conventional, interference-measurement based, dynamic channel assignment (DCA) algorithms. The basic idea is to use interbase signaling to shift most of the burden of the resource allocation from the air interface to the backbone infrastructure. By exchanging channel assignment as well as other relevant information in real time through the backbone network, each base can calculate the impact of a resource assignment on the system. As a result, rapid interference measurements, which are typically needed to implement DCA schemes, are replaced by a limited amount of path loss measurements and the computation of interference conditions by the base stations. This significantly reduces the measurement and over-the-air signaling requirements, and can also provide an opportunity for a better optimization of the system performance. We focus on two specific algorithms: network-assisted least-interference-based dynamic packet assignment (NA-LI-DPA) and network-assisted dynamic packet assignment with throughput optimization (NA-DPA). NA-LI-DPA closely resembles a least-interference-based dynamic channel assignment algorithm, and NA-DPA attempts to further improve the overall system throughput. The algorithms, as defined, are appropriate for a best-effort data service, where the primary goal is to provide a higher throughput. However, it will be clear from the discussion that it is also feasible to alter the algorithms to optimize performance metrics other than throughput, e.g., to ensure a certain quality of service. We show through simulation that, for a system like enhanced general packet radio service (EGPRS) system, NA-DPA can provide a throughput that is 50% higher than random packet assignment, and 25% higher than that obtained by conventional DCA algorithms.

In the project FRAMES (Future Radio Wideband Multiple Access Systems) of the European research program ACTS (Advanced Communications Technologies and Services) an air interface proposal for UMTS (Universal Mobile Telecommunications System) has been developed. In January 1998 ETSI (European Telecommunications Standards Institute) reached a consensus on a UMTS air interface standard termed UTRA (UMTS Terrestrial Radio Access), which is mainly based on the proposal developed within FRAMES. UTRA consists of an FDD (frequency division duplex) mode applying the multiple access scheme W-CDMA (wideband CDMA) and a TDD (time division duplex) mode applying the multiple access scheme TD-CDMA (time division CDMA). For the different services to be supported a set of channel coders has been proposed which have to be further evaluated. In consideration of this need, in this paper a low-complexity rate-compatible punctured turbo code (RCPTC) for high-quality circuit switched data services in the TDD-mode is investigated depending on its main parameters. The criterion in these investigations is the bit error ratio (BER). The performance of the considered turbo code (TC) is analyzed and compared to a convolutional code (CC) of equal complexity.

The present paper introduces frequency domain equalisation (FDE) as an efficient means for single‐user detection (SUD) in universal mobile telecommunication systems (UMTS) handhelds. Such an SUD is, at least partially, able to remove multiple access interference (MAI) like a multi‐user detector (MUD), however with several important advantages the operation principle of an FDE‐SUD is simple and easy to understand, the FDE‐SUD shows low numerical complexity and therefore, it is not power hungry like an MUD. The problem of applying FDE without zero‐padding or cyclic‐prefix insertion is solved by using the overlap‐cut method. In this paper we also prove that the performance of the FDE‐SUD is practically identical to that of linear MUD for a fully loaded UMTS cell. Furthermore, armed with the idea of FDE for code division multiple access (CDMA), we can construct a common receiver structure for CDMA, time division multiple access (TDMA), orthogonal frequency division multiplexing (OFDM) and multi‐carrier CDMA (MC‐CDMA) systems. This is an extremely useful idea in enabling a software‐defined radio (SDR) which can operate seamlessly in several environments such as UMTS, the IEEE 802.11a and WiMaX. FDE based receivers could be one important building‐block for the next generation mobile communications. Copyright © 2008 John Wiley & Sons, Ltd.

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>

We propose a time division multiple access (TDMA) scheme for the BPSK modulated single carrier block transmission with frequency domain equalization (SC-FDE) over ultra-wideband (UWB) communications. The transmitter and receiver matrices for the proposed TDMA SC-FDE system are derived to achieve the multiple access interference (MAI) free and interblock-interference (IBI) free transmission without the insertion of cyclic prefix (CP) between blocks, circumventing the need for long CP and large FFT size in high speed UWB communications. The performance of the proposed TDMA SC-FDE system over UWB channels is investigated and compared with that of the block spread code division multiple access (CDMA) scheme. The effects of oversampling diversity and imperfect channel estimation are also investigated. Results show that the proposed TDMA scheme can effectively eliminate the error floor in CDMA due to insufficient CP, and it is more efficient to accommodate larger number of users than CDMA in high data rate transmission

We examine systems of fixed-channel reuse for base stations in an indoor infrared wireless communication system. The following techniques are compared: time-division multiple access (TDMA) using on-off keying (OOK) or pulse-position modulation (PPM); frequency-division multiple access (FDMA) using binary phase-shift keying (BPSK) or quadrature phase-shift keying (QPSK); code-division multiple access (CDMA) using OOK with direct-sequence spreading by m-sequences or optical orthogonal codes (OOCs). We define a parameter /spl gamma/, which equals the signal-to-noise ratio (SNR) for unit optical path gain and is proportional to the square of the transmitted average optical power. Using measured pathloss data, it is found that in a system using hexagonal cells and a reuse factor of three, for cell radii above 3 m, TDMA with OOK or 2-PPM, and CDMA using OOCs all require approximately the same /spl gamma/ to achieve a worst-case bit-error rate (BER) of 10/sup -9/ within a cell. Using TDMA with 4-PPM results in a 6-dB decrease in the required value of /spl gamma/. CDMA using m-sequences requires an increase in /spl gamma/ of 5 dB over TDMA using OOK, and FDMA with BPSK requires an increase of 12 dB. For a given reuse factor N in the noise-limited regime, the required value of /spl gamma/ decreases in inverse proportion to N/sup 2/ for TDMA schemes and inversely with N for FDMA and CDMA schemes. For cell radii below 3 m, cochannel interference dominates the systems using TDMA, FDMA, and CDMA with an OOC, resulting in an irreducible BER above 10/sup -9/ at cell radii below 1.5 m. Only CDMA with m-sequences does not develop an irreducible BER, making it the only choice for cell radii below 1.5 m.

Code division multiple access (CDMA) promises to become the enabling technology for the future generation of satellite communications. For instance, CDMA is being used in Globalstar, Skybridge and is also proposed for the satellite component of UMTS. The evolution of satellite systems towards multimedia communications, necessitates not only wideband CDMA but also requires a hybrid code and time division multiple access (CTDMA) technique because of the packet nature of the data. In this paper, we give an overview of the challenges in designing a wideband CTDMA modem. As a first challenge, the wideband nature of the CDMA modem dictates that the tracking loops of the modem can no longer be executed in software but must be fully integrated in VLSI. Second, the packet based nature of the communication in a CTDMA modem requires ultra fast acquisition for each packet. The extremely low signal-to-noise ratio in satellite communications largely complicates this fast acquisition task.

In this paper, a comparison study of various UMTS data transmission techniques is performed. An analysis of the system in the presence of geographically non-uniform multi-service traffic profiles is done for three transmission techniques: Frequency Division Duplex (FDD), Time Division Duplex (TDD), and High Speed Downlink Packet Access (HSDPA). Several combinations were selected: FDD, TDD, FDD combined with HSDPA, FDD combined with TDD, and FDD combined with TDD and HSDPA. The TDD mode is the technique with better results, but the introduction of HSDPA is clearly beneficial for data services, as expected. The distribution of the services by the three techniques is the best scenario, namely for some traffic profiles. For example, for a threshold of 128 kbps (for HSDPA services) and 50 % of the power reserved to HSDPA, it is possible to get 1.4 GB of carried traffic.

The authors present a novel cell structure that combines the qualities of code division multiple access (CDMA) and time division multiple access (TDMA) to reduce cochannel interferences. The cell consists of a centrally located base station with eight surrounding corner antennas. The mobiles and antennas operate in a TDMA mode and the communication channels employ spread spectrum direct sequence modulation. TDMA combined with the spatial separation of the cell antennas reduces the carrier-to-interference ratio and thereby increases the cell capacity. The capability and cochannel interference for both forward and reverse link of the proposed system are computed and compared with that of the traditional CDMA cellular system. The results show that the capacity of the proposed system in the forward link is increased by an average factor of three over the traditional CDMA cellular system. For the reverse link the capacities of the systems are comparable. >

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. >

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.

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.

The standard time division multiple access (TDMA) cellular network is designed so that physically adjacent cells are assigned different frequency bands, or channels, in order to reduce inter-cell interference. A multiple-access scheme is presented in which TDMA is used inside each cell, but different transmitted pulse shapes with low cross-correlations are assigned to adjacent cells. These pulses could be direct-sequence spread-spectrum pulses, which have been proposed for code division multiple access (CDMA) wireless networks. Such a hybrid system combines the high intra-cell capacity of TDMA with the inter-cell and multipath interference rejection capabilities of CDMA. It is concluded that this hybrid scheme offers a potential increase in capacity relative to intra-cell TDMA/inter-cell frequency-division multiple access (FDMA) provided that interference suppression techniques can be used to suppress inter-cell interference. Additional advantages and disadvantages of the scheme are discussed.

For future mobile communications, an appropriately chosen multiple access scheme is a critical issue. To support robust frequency planning, multi-operator scenarios, system coexistence and hierarchical cell structures, frequency division multiple access (FDMA) and multicarrier techniques are viable choices. Further multiple access schemes presently under discussion are code division multiple access (CDMA) and time division multiple access (TDMA). A mobile radio system concept deploying a hybrid frequency and time divided code division multiple access (F/T/CDMA) scheme with a multicarrier CDMA (MC-CDMA) component, called MC/JD-CDMA, is proposed and performance results for the uplink are presented. Attractive features of the proposed system concept are the possibility to flexibly offer voice and data services with different bit rates, soft capacity, as well as inherent frequency and interferer diversity.

Chapter 6 - Digital & Digital/Analogue Communications Systems