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Spread Spectrum Techniques and Applications, 2002 IEEE Seventh International Symposium on

Date 2-5 Sept. 2002

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  • 2002 IEEE Seventh International Symposium on Spread Spectrum Techniques and Applications [front matter]

    Page(s): I - XIX
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    Freely Available from IEEE
  • Author index

    Page(s): XX - XXIII
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  • Determining code symbol LLRs on diversity channels with applications to cdma2000

    Page(s): 807 - 811 vol.3
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    The reverse link of cdma2000 uses a code-multiplexed pilot signal to allow for near coherent demodulation at the base station receiver. Typical RAKE receivers approximate maximal ratio combining by using a "pilot filter" to derive a combiner weight estimate from the noisy pilot signal. It is possible to improve on this design by exploiting the channel information that is also embedded in the encoded data-bearing signal. We show how the pilot and data-bearing signals may be used to determine, implicitly, "combiner weights", and explicitly, code symbol log likelihood ratios (LLRs). Simulation results on the cdma2000 reverse link demonstrate SNR gains on the order of 0.5 dB with the default pilot-to-traffic ratios. Even larger gains may be achieved by optimizing the pilot-to-traffic ratio appropriately. View full abstract»

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  • Error rate performance bounds in block coded parallel combinatorial SS systems through a uniform interleaver

    Page(s): 736 - 740 vol.3
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    Upper bounds on the codeword and bit error probabilities are obtained for maximum-likelihood (ML) decoding of block coded parallel combinatorial spread spectrum (PC/SS) systems in additive white Gaussian noise (AWGN) channels. To make the analysis tractable, we put a uniform interleaver between a block encoder and a PC/SS transmitter. An input-output distance enumerating function (IODEF) is introduced to calculate the number of codewords for an overall coded PC/SS system instead of the input-output weight enumerating function (IOWEF). The average bounds on the bit error rate (BER) of block coded PC/SS systems on AWGN channels are shown. It is demonstrated that the performance advantage between PC/SS systems is determined by the number of information bits per active transmitting PN code. A comparison between the coded PC/SS systems and coded conventional multicode DS/SS systems is also discussed. View full abstract»

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  • A systematic approach to code phase acquisition in DS-CDMA

    Page(s): 741 - 745 vol.3
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    A new approach to the problem of code phase acquisition is presented. The proposed search strategy is formulated in terms of a single correlator device, and a comparison to the traditional serial search is performed. The new strategy combines two processes. First, there is a sorting part which converges to the most probable delay in a statistical sense. As a second part, a detection process is performed. Combining both parts results in a systematic acquisition process. It appears that the proposed algorithm is insensitive to the received signal's initial code phase. Using the proposed approach reduces the mean and, essentially, the variance of the time-to-first-fix (TTFF), resulting in an efficient and reliable acquisition process. View full abstract»

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  • Serially concatenated coding for broadcasting S-UMTS applications

    Page(s): 697 - 701 vol.3
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    Satellite-UMTS supports broadcast applications that involve transmission of the same encoded data over channels that may vary significantly. The same code must allow a user with a good channel to recover the information with low complexity, while a user with a bad channel should still be able to achieve an acceptable BER at the cost of increased complexity and/or decoding delay. To this end, we propose serially concatenated multilevel code structures that employ PSK modulation. The receiver has the flexibility to achieve turbo-code, trellis-code or uncoded performance, depending on the decoding effort. Design considerations include the constituent encoder design and the use of a non-uniform constellation. Simulation results investigate the system's performance and highlight different parameters trade-offs. View full abstract»

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  • Multipath resolution with PN chip interval

    Page(s): 746 - 750 vol.3
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    If the delay between two multipaths is about a chip interval and the path strength is almost equal, then the envelope tracking (ENV) scheme of A. Baier et al. (see IEEE JSAC, vol.12, no.4, p.733-43, 1994) performs poorly. This is because only a single peak is observed in the envelope of the correlation function (or multipath power delay profile) and the peak position is about half a chip interval away from the two true multipath delays. Also, the envelope tracking with subtraction (ENV-SUB) scheme of E. Sourour et al. (see Proc. IEEE 49th VTC, p.422-6, 1999) regards the channel in this situation as a three-path channel and generates incorrect delay estimates. K. Han et al. (see ICC, 2001) proposed a heuristic multipath searcher for this situation. We propose a multipath searcher with a chip time resolution for such a two-path channel with near-equal strength, based on the maximum likelihood (ML) principle. In addition, the paper presents the detection probability that a two-path channel decision is made when the channel has two paths truly, given that the multipath delay power profile shows a single peak. The analytical results are compared with those of Han et al. View full abstract»

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  • FFT-speed and windowed multiuser detector for UTRA-FDD high rate data mode

    Page(s): 712 - 716 vol.3
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    The family of international standards for mobile. communications, IMT-2000, includes, amongst others, the universal terrestrial radio access (UTRA) proposal, which consists of two modes: frequency division duplex (FDD); time division duplex (TDD). A new approach based on the zero-forcing multiuser detector (ZF-MUD) is investigated for the high rate data mode in the UTRA-FDD uplink. This approach is compared to the FFT speed ZF-MUD (see Machauer, R. et al., Proc. IEEE 54th Vehicular Technology Conf., p. 502-5, 2001) which was originally introduced by M. Vollmer et al. (see Proc. Int. Conf. on Telecom., ICT, 1999) for use in UTRA-TDD. The multiple access interference (MAI) and intersymbol interference (ISI) reduction of these multiuser detectors leads to a high BER gain compared to the RAKE receiver. The computational complexity is reduced by taking advantage of the UTRA-FDD structure. Both algorithms can easily be adapted to parallel computation. View full abstract»

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  • Generalized closed loop transmit diversity algorithm for WCDMA

    Page(s): 797 - 801 vol.3
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    A previously proposed transmit diversity algorithm for four antennas is extended to an algorithm for eight transmit antennas. Depending on a signal-to-interference-plus-noise ratio maximization criterion, either full (all available transmit antennas) or partial diversity (only a subset or all available transmit antennas) is used. Phase adjustments are also applied between the selected antennas. The proposed algorithm offers a considerable gain in transmit signal-to-noise ratio per bit compared to all-antenna transmission and one-antenna selection transmit diversity. The gain is present for both uncorrelated fading and for correlated fading between transmit antennas. Furthermore, it has been shown that the proposed algorithm is more robust to the channel estimation errors than an all-antenna transmit diversity or one-antenna selection transmit diversity. View full abstract»

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  • Evaluation of throughput and coverage employing multipath interference canceller in high-speed downlink packet access in multipath fading channel

    Page(s): 667 - 671 vol.3
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    This paper presents the throughput performance based on system-level simulations employing essential techniques, e.g.. the adaptive modulation and channel coding (AMC) scheme and the fast scheduling algorithm, in high-speed downlink packet access called HSDPA in a multipath fading channel. The computer simulation results elucidate that the multipath interference canceller (MPIC), which we previously proposed, exhibits a sufficient multipath interference (MPI) suppression effect especially for the use of multi-level modulation such as 16QAM and 64QAM, resulting in increased overall throughput. We also show that the average throughput above 10 Mbps and 5 Mbps are possible for approximately 15 and 50% of users employing, a matched filter (MF)-based RAKE receiver within a cell in a one-path channel, respectively Furthermore, we clarify that although, in a two-path filling channel, the probability of users using the MF-based RAKE receiver who can satisfy the average throughput above 5 Mbps is reduced to approximately 15% within a cell, it can be increased to approximately 30% by employing MPIC thanks to its effective MPI suppression. View full abstract»

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  • Performance evaluation of quantum based multi-user detector

    Page(s): 722 - 725 vol.3
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    Future wired and wireless communication systems will employ pure or combined code division multiple access (CDMA) techniques, such as in the European 3G mobile UMTS or power line communications system, but also several 4G proposals include, for example, multicarrier (MC) CDMA. Previous investigations discovered the drawbacks of single user detectors (SUD), which are widely employed in narrowband IS-95 CDMA systems, and were forced to develop suitable multiuser detection schemes to increase the efficiency against interference. However, at this moment there are only suboptimal solutions available became of the rather high complexity of optimal detectors. One of the possible receiver technologies may be quantum assisted computing devices which allow high level parallelism in computation. The first commercial devices are estimated for the next years, which meets the advent of 3G and 4G systems. We analyze the error probability and give tight bounds in a static and dynamically changing environment for a novel quantum computation based quantum multi-user detection (QMUD) algorithm, employing a quantum counting algorithm, which provides an optimal solution. View full abstract»

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  • Ultra low current consumption 2.4 GHz DS-SS radio modem

    Page(s): 817 - 821 vol.3
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    SS radio communication systems in 2.4 GHz ISM band, such as IEEE802.11 and Bluetooth are widely known. These systems can provide very high data rate, over several Mbps. However, on the other hand, they have problems such as high current consumption, short range service area, large size, high design expenditure and development difficulty. From the view point above, to solve these problems, we developed an ultra low current consumption 2.4 GHz DSSS radio modem, which consumes 35 mA current at full rate, in a small size and for a wide service area. Although the current consumption was extremely low, the receiver sensitivity and intermodulation-distortion performance were qualified. A sufficient performance was obtained from actual measurement of the system. View full abstract»

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  • A novel hardware design paradigm for mobile 'software defined radio' terminals

    Page(s): 828 - 831 vol.3
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    On the way to mobile software defined radio terminals (SDR terminals), a change of the design philosophy for appropriate microelectronic hardware is necessary. The desired reconfigurability must be provided under the constraints of a low power consumption, a low bill of materials, and a small size. This contribution proposes a novel design paradigm for hardware development, which will help to pave the way for software defined radio terminals. View full abstract»

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  • Introducing delay sensitivity into the proportional fair algorithm for CDMA downlink scheduling

    Page(s): 652 - 656 vol.3
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    The paper is concerned with CDMA base stations needing forward link scheduling algorithms that not only maximize total throughput given certain constraints regarding fairness, but that also take into account the special delay requirements of real time data. We show that the proportional fair algorithm, which was originally designed to maintain fairness while still exploiting channel variations in a fading environment, can be modified in a simple manner so as to ensure the successful delivery of real time data without giving up the gains due to channel diversity. View full abstract»

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  • A simple iterative power control scheme for successive interference cancellation

    Page(s): 761 - 765 vol.3
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    Successive interference cancellation (SIC) is a technique which has the potential to increase the capacity of DS-CDMA systems substantially. One of the major criticisms of the technique is that it requires a specific distribution of unequal received powers from the mobile units. In the presence of estimation error, the required distribution becomes even more complicated and it is critical that the users adapt to these required power levels in order to achieve good system performance. In this paper, a simple iterative technique based on the existing power control algorithm for commercial CDMA systems is presented. This algorithm is shown to converge to the optimal power control solution for SIC, mathematically for a static channel, and with simulations for a fading channel. Convergence is considered as a function of important system parameters such as estimation error, power control step size, Doppler frequency, and the number of users in the system. The surprising conclusion is that power control for a realistic successive interference cancellation system doesn't require additional complexity relative to a conventional CDMA system. View full abstract»

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  • Combined DSSS/FHSS approach to interference rejection and navigation support in UAV communications and control

    Page(s): 687 - 691 vol.3
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    Unmanned aerial vehicles (UAVs) for a wide variety of applications have enjoyed growing interest. One of the most critical component of a UAV system is the datalink between the UAV itself and the ground control station. This paper provides a comprehensive overview of the requirements for medium-range UAV data links. Special emphasis is given to requirements and solutions which are related to the application of spread spectrum techniques. Based on the analysis of requirements and possible design solutions, the system concept and the hardware structure of a production-stage datalink system for a medium-range UAV carrying an electro-optical sensor payload is presented. View full abstract»

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  • Performance of EM-based multiuser detection for space-time block coded WCDMA systems over multipath fading channels

    Page(s): 707 - 711 vol.3
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    We present a multiuser detection (MUD) scheme derived from the expectation maximization (EM) algorithm for the downlink of space-time block coded (STBC) WCDMA systems. We consider the downlink scenario with two transmit antennas and a single receive antenna and multipath fading channels. The EM-based MUD looks iteratively for the maximum-likelihood solution. Its structure is very similar to the parallel interference cancellation (PIC) receiver but with better convergence properties. Our simulation results show significant performance gains over conventional and PIC receivers. View full abstract»

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  • Transmit diversity for frequency selective channels in UMTS-TDD

    Page(s): 802 - 806 vol.3
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    Multipath propagation and fading are typical characteristics of wireless communication channels. Simultaneously, they are also the most limiting factors for high speed data rates. The paper investigates the performance of systems using multiple transmit antennas (MISO - multiple input single output) in frequency-selective channels, which combat fading and exploit multipath propagation. The system considered is UMTS-TDD. The investigations focus on different antenna configurations and on correlated propagation channels. The impact of Doppler-spread due to the velocity of the mobile user is considered. The problem of asymmetrical data-rates on uplink and downlink is addressed. View full abstract»

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  • Possibilities of the use of SAW technology in future wireless access networks

    Page(s): 832 - 836 vol.3
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    The use of solid state technologies are considered , in particular acousto-electronic (AE) and planar acousto-optic (AO) technologies for the analog pre-processing of spread spectrum signals in multiple wireless access systems. The long term studies show the potential of the proposed approaches to an advanced air-interface architecture based on the solid state electronics to meet the requirements for future mobile and fixed wireless networks. View full abstract»

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  • Automatic selection of window add in a WCDMA radio network based on cost function minimization

    Page(s): 672 - 676 vol.3
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    WCDMA networks have many parameters which determine their performance. Ensuring a desired quality of service means a proper choice of parameters. One approach to choosing these parameters automatically is to minimize a cost function with respect to these parameters. The minimum of the cost function corresponds to an optimal network performance. The choice of cost function, in the simplest case can be some combination of key performance indicators (KPIs) of the network. Here a cost function is described which can be used to minimize the value of one of these KPIs, the call blocking rate in the network. A second order gradient method is derived which is used to minimize the cost function. The cost function and gradient algorithm are implemented on an advanced WCDMA radio network simulator to optimize the value of the soft handover parameter window add. View full abstract»

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  • MUSYCA: a quasi synchronous CDMA VLSI processor and its application to multiple access

    Page(s): 822 - 827 vol.3
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    Quasi synchronous CDMA (QS-CDMA) is a quite well known technique which offers both the flexibility of a CDMA (access and resource management techniques) and the capacity of a TDMA system. QS-CDMA is advantageous if the propagation channel is near from line of sight and if the coherence time is high. Hence QS-CDMA has formerly been proposed for GEO satellite and cable modem uplink communication. An implementation of a QS-CDMA digital processor is proposed along with a test platform and performances evaluation. This PHY layer chip is able to handle a large number of simultaneous users, proposes an original connection mechanism and also provides all control information for the MAC layer. It offers a great flexibility due to its high programmability. An application to the uplink of a cable modem is proposed. View full abstract»

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  • Performance of hybrid ARQ techniques based on turbo codes for high-speed packet transmission

    Page(s): 682 - 686 vol.3
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    Since the asymmetric service is the focus on the future mobile communications, Internet services such as downloads of large data files from Web sites have been gaining popularity. Reliable high-speed (2 Mbps and above) downlink packet transmission becomes a topic of great interest. Hybrid ARQ is one of such techniques which can be used to provide reliable packet transmission. In this paper, different hybrid ARQ techniques, namely Type III multiple redundancy, Type II incremental redundancy, Type I with and without packet combining and Type I with soft information (SI) based on turbo codes are compared. Comparisons between turbo codes and convolutional codes for each hybrid ARQ technique are also investigated. Moreover, the complexity of different hybrid ARQ technique is evaluated afterwards. The results show that Type II incremental redundancy hybrid ARQ technique based on turbo codes gives the best throughput performance at the cost of larger memory requirement. It is more suitable for future high-speed packet transmission where the memory requirement is not so crucial. Type III multiple redundancy based on turbo codes achieves the second best throughput performance with each transmission self-decodable. It is more suitable for certain applications such as deep space communications. Type I with packet combining technique achieves the relatively better throughput performance with less memory requirement. It is more suitable for applications where memory is the most crucial. View full abstract»

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  • Construction of a multi-mode receiver for various spread spectrum communication and broadcasting systems

    Page(s): 837 - 841 vol.3
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    We investigate a construction of a multi-mode receiver for various spread spectrum communication and broadcasting systems. We propose a way to reduce the hardware scale by sharing the same IF-unit. Therefore, it is possible to minimize the increase of the total bandwidth of the IF signal. We assume a receiver tuned to IMT-2000, 2.6 GHz satellite broadcast system and IEEE 802.11 wireless LAN for the proposed method, and consider IF carrier positioning and the system power ratio. Through computer simulation we show that the IF-unit is shared without increasing the bandwidth as much as it is done in conventional systems. View full abstract»

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  • Mutual interference of IMT-2000 networks

    Page(s): 657 - 661 vol.3
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    We consider the adjacent channel interference of IMT-2000 networks. The results are shown for the UTRA-FDD mode of the IMT-2000 standard but can be applied to any other mode. The interference is described by an analytical model which includes all interference sources in a cluster of 7 cells. This interference calculation is used to describe the capacity loss caused by neighboring IMT-2000 network operators. The capacity loss is calculated as a function of the location distance of the base stations and the number of users. The simulations show the well known result that the coordination of the positioning of the networks is a key task to improve the network performance and to utilize the expensive spectrum efficiently. Additionally, we show that baseband filtering has a big impact on the capacity. We show this effect by comparing the cdma2000 against the UMTS UTRA-FDD standard. View full abstract»

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  • Power control in CDMA interference-shared return-links subject to large delays

    Page(s): 766 - 771 vol.3
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    The use of power control for interference-shared CDMA links is well understood. But performance suffers when those links have large delays. We analyze that performance and show how the poor performance can be ameliorated. View full abstract»

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