| 1. |
- Cresp, Gregory, et al.
(författare)
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Bit Error Rates of Large Area Synchronous Systems
- 2008
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Konferensbidrag (refereegranskat)abstract
- Large Area Synchronous (LAS) sequences are a class of ternary interference free window spreading sequences. One of their advantages is the ability to construct permutation LAS families in order to reduce adjacent cell interference (ACI) in cellular systems. There has been little previous numerical work to examine the effect of using permutation families compared to simply reusing the same LAS family across different cells. The bit error rates resulting from two cell systems employing both permutation families and sequence reuse are considered here by simulation.
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| 2. |
- Cresp, Gregory, et al.
(författare)
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Combination Oppermann Sequences for Spread Spectrum Systems
- 2005
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Konferensbidrag (refereegranskat)abstract
- Numerous spread spectrum applications require families of long spreading sequences, often used at very high chip rates. In this paper, an algebraically simple way of generating long sequences by combining shorter polyphase sequences is presented, aimed at asynchronous spread spectrum systems. The approach is motivated by the fact that polyphase sequences offer increased design options, in terms of the supported range of correlation characteristics, while combination sequences allow for simpler generation of long sequences. It leads to the definition of combination Oppermann sequences, the properties of which are investigated in this paper. Numerical results indicate that the families of these proposed combination sequences provide favourable aperiodic correlations. The presented family of combination Oppermann sequences is therefore suitable for applications that rely on rapid synchronisation and are required to provide multiple access to the system.
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| 3. |
- Cresp, Gregory, et al.
(författare)
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Design of Modified UCHT Sequences
- 2006
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Konferensbidrag (refereegranskat)abstract
- In this paper, we consider the design of a class of unified complex Hadamard transform (UCHT) sequences. An effi- cient modification is imposed to those sequences to better suit applications in asynchronous code-division multiple- access (CDMA) systems. These modified UCHT sequences preserve the orthogonality of the original UCHT sequences and offer increased design options due to an increased number of parameters. The design of UCHT, modified UCHT, and Oppermann sequences is then formulated with reference to optimizing the maximum nontrivial aperiodic correlation value. These optimization problems can then be solved efficiently using a genetic algorithm with the maximum nontrivial aperiodic correlation value serving in the definition of a fitness function. Numerical examples illustrate the benefits of modified UCHT sequences over the original UCHT sequences.
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| 4. |
- Cresp, Gregory, et al.
(författare)
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Design of Sequence Family Subsets Using a Branch and Bound Technique
- 2009
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Ingår i: IEEE Transactions on Information Theory. - : IEEE. - 0018-9448 .- 1557-9654. ; 55:8, s. 3847-3857
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Tidskriftsartikel (refereegranskat)abstract
- The number of spreading sequences required for Direct Sequence Code Division Multiple Access (DS-CDMA) systems depends on the number of simultaneous users in the system. Often a sequence family provides more sequences than are required; in many cases the selection of the employed sequences is a computationally intensive task. This selection is a key consideration, as the properties of the sequences assigned affect the error performance in the system. In this paper, a branch and bound algorithm is presented to perform this selection based on two different cost functions. Numerical results are presented to demonstrate the improved performance of this algorithm over previous work.
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| 5. |
- Cresp, Gregory, et al.
(författare)
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On the Classification of Large Area Sequences
- 2007
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Konferensbidrag (refereegranskat)abstract
- Large Area (LA) sequences form a class of ternary spreading sequences which exhibit an interference free window. In addition, these sequences have low correlation properties outside this window. Work to date has concentrated on examining the parameters and performance of LA sequences with reference to only a small number of example families. In this paper we develop general conditions which an LA family must satisfy. The development of these conditions allows for the production of computationally efficient tests to determine whether a given family is an LA family. In particular, these tests can form the basis for algorithms to construct LA families, allowing for a larger number of families with the potential for higher energy efficiency than those of previous work.
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| 6. |
- Cresp, Gregory, et al.
(författare)
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Periodic Oppermann Sequences for Spread Spectrum Systems
- 2005
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Konferensbidrag (refereegranskat)abstract
- In this paper we introduce periodic Oppermann sequences, which constitute a special class of polyphase sequences. The properties of these sequences are presented, and indicate that periodic Oppermann sequences are suitable for combination to generate families of longer sequences. Numerical examples show that periodic Oppermann sequences can be designed for ranging or synchronisation applications or for supporting multiple access spread spectrum communication systems.
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| 7. |
- Cresp, Gregory, et al.
(författare)
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Subset Family Design Using a Branch and Bound Technique
- 2006
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Konferensbidrag (refereegranskat)abstract
- The number of spreading sequences required for Direct Sequence Code Division Multiple Access (DS-CDMA) systems depends on the number of simultaneous users on the channel. The correlation properties of the sequences used affect the bit error rate of the system. Often a sequence family provides more sequences than are required and in many cases the selection of the employed sequences is a computationally intensive task. In this paper, a branch and bound algorithm is presented to optimise the subset of available sequences given the required subset size. In contrast to previous approaches, the resulting subset is guaranteed to be optimal. Numerical results are presented to demonstrate the improved performance of this algorithm over previous work.
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| 8. |
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| 9. |
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| 10. |
- Dam, Hai Huyen, et al.
(författare)
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Blind MIMO Equalization in the Frequency Domain
- 2005
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Konferensbidrag (refereegranskat)abstract
- Broadband wireless systems require low complexity equalizers which can cope with long channel impulse responses and severe intersymbol interference (ISI). In this paper, a frequency domain (FD) approach for adaptive blind equalization for multiple-input multiple-output (MIMO) communication systems is proposed. As an initial step, a time domain (TD) block based updated adaptation is first developed which updates the equalizer coefficients once per each block of data symbols. As such, this algorithm can be equivalently implemented in the FD to reduce computational complexity associated with the symbol by symbol TD update. Simulation results show that the proposed algorithms can successfully separate and equalize the received signals with a significantly lower computational complexity than a corresponding TD approach.
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