| 1. |
- Ben Slimane, Slimane
(författare)
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OFDM Schemes with Non-Overlapping Time Waveforms
- 1998
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Ingår i: Vehicular Technology Conference, 1998. VTC 98. 48th IEEE. - New York : IEEE. - 0780343204 ; , s. 2067-2071
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Konferensbidrag (refereegranskat)abstract
- For orthogonal frequency division multiplexing (OFDM) schemes, the time waveform plays a major role not only in shaping the spectrum of the transmitted signal but also in separating the signal subcarriers at the receiver. The selection of such waveform is then very important and can make a big difference in spectrum utilization and system performance. The difficulty in using pulse shaping with OFDM appears in the detector design since smooth time waveforms destroy the orthogonality between subcarriers and introduce inter-channel interference (ICI). This paper investigates the use of non-overlapping signal waveforms for OFDM schemes. It is shown that pulse shaping for such schemes can be equivalently achieved using a discrete shaping matrix. Such a shaping structure is very suitable for digital implementation and can be combined with OFDM schemes without affecting their IDFT/DFT operators. It therefore makes the use of guard time interval (cyclic prefix) for OFDM schemes possible with any kind of non-overlapping shaping waveform.
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| 2. |
- Nilsson, Rickard, et al.
(författare)
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A low complexity threshold detector making MLSD decisions in a multiuser environment
- 1998
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Ingår i: Pathway to a global wireless revolution. - Piscataway, NJ : IEEE Communications Society. - 0780343204 ; , s. 333-337
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Konferensbidrag (refereegranskat)abstract
- In this paper we present a pipelined implementation of an iterative threshold detector, which makes the same decisions as a maximum likelihood sequence detector (MLSD) on some, but not necessarily all, bits. We apply this as a first stage detector in a direct sequence code division multiple access (DS-CDMA) interference-limited multiuser system. In combination with the single-user matched filter (MF) detector we obtain improved performance and lower complexity than with the decorrelating receiver for a limited number of simultaneous users, e.g. up to 25 users with a spreading factor of 127.
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| 3. |
- van de Beek, Jaap, et al.
(författare)
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Synchronization of a TDMA-OFDM frequency hopping system
- 1998
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Ingår i: Pathway to a global wireless revolution. - Piscataway, NJ : IEEE Communications Society. - 0780343204 ; , s. 1290-1294
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Konferensbidrag (refereegranskat)abstract
- In this paper we present a Time Division Multiple Access-Orthogonal Frequency Division Multiplexing (TDMA-OFDM)-based radio interface proposal for the Universal Mobile Telecommunication System (UMTS). We focus on synchronization and present an implementable algorithm for the tracking of the mobiles' time and frequency offsets at the base station in the uplink. This algorithm is based on recently developed estimation methods that use redundancy introduced by the cyclic prefix. A modified Maximum Likelihood (ML) estimator for the Additive White Gaussian Noise (AWGN) channel is used to meet both implementational requirements and performance requirements for frequency-selective fading multiuser environments. Simulation results for a typical UMTS mobile channel environment show that the uncoded symbol error rate of a coherently modulated system using our synchronization scheme is virtually indistinguishable from that of a system with no time and frequency offset.
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