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| 2. |
- Dam, Hai Huyen, et al.
(author)
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Complex Spreading Sequence Design
- 2002
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Conference paper (peer-reviewed)abstract
- The performance of code division multiple access system depends on the correlation of the employed spreading code. Low cross-correlation values between spreading sequences are desired to suppress multiple access interference. An auto-correlation function with with a distinct peak enables proper synchronization and suppresses intersymbol interference. However, these requirements contradict each other and a trade-off needs to be established. In this paper, a global two dimensional optimization method is proposed to minimize auto-correlation with cross-correlation being allowed to lie within a fixed region. This approach is applied to design a set of complex valued spreading sequences.
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| 3. |
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| 4. |
- Dam, Hai Huyen, et al.
(author)
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Non-Causal Delayless Subband Adaptive Equalizer
- 2002
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Conference paper (peer-reviewed)abstract
- In wireless communication, multiple versions of the transmitted signals arrive at the receiver with different attenuations and time delays. Thus, an equalizer with long filter is required at the receiver to reverse the multipath effects. In this paper, a new non-causal delayless subband equalizer structure is proposed to reduce the computational complexity of the equalizer and to improve the channel tracking capability. This structure avoids the additional delays usually associated with the subband schemes. A design method is formulated to minimize the aliasing effect of the filter bank in the subbands. The significance of employing a non-causal equalizer is also emphasized. Simulation results show that the performance of the new structure is significantly improved by using the design method. Moreover, the complexity of the new subband equalizer is a fraction of the equivalent fullband at the expense of small degradation in the performance.
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| 5. |
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| 6. |
- Grbic, Nedelko, et al.
(author)
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A New Pilot-Signal based Space-Time Adaptive Algorithm
- 2001
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Conference paper (peer-reviewed)abstract
- In the application of adaptive antenna arrays to wireless communications, a known pilot signal sequence may be used for estimating the array response at the beginning of each data frame. This pilot sequence is usually very short and conventional training methods which estimate the array response, based solely on this training sequence, may incur large estimation errors. In this paper, we propose an online modified weighted recursive least squares type of training algorithm for estimating the optimal array response by exploiting information from the whole frame of the received signal. The benefits of the proposed algorithm is that tracking of coherent noise and interference signals is substantially improved, and the overall performance is increased. Simulation results show that the proposed method offers substantial improvement when compared to the conventional least squares method.
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| 7. |
- Nordberg, Jörgen, et al.
(author)
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A Blind Closed Loop Subband Channel Equalizer
- 2004
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Conference paper (peer-reviewed)abstract
- The wireless communication channel are characterized by its multipath richness, specially in the unlicensed 60 GHz band where many of the modern and future wireless communication system will work. To reverse the effects of even a moderate delay spread, in the linear equalization case, will require an estimation of high order filters. Thus, there will be a demand for low complexity high quality receivers that should be able to work during sever multipath conditions. In this paper, a new blind closed loop subband equalizer is proposed to reduce the computational complexity of the equalizer and also to improve the channel tracking capability. Simulation results show a significantly improvement, 12 times, of the convergence rate without any significant performance loss.
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| 8. |
- Nordberg, Jörgen
(author)
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Blind Subband Adaptive Equalization
- 2002
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Reports (other academic/artistic)abstract
- It is predicted that a large portion of future wireless communication capacity will be used to provide wireless data services. This new emphasis results in a significant change in substantial parts of the wireless infrastructure, it is important to have low bit error transmission links to get Quality of Service similar to the internet. Future services will also demand higher data rates. These factors mean that there will be a significant need for good quality equalization schemes in the receiver to reduce the different effects of the radio channels, such as intersymbol interference and multipath propagation. The use of linear equalizers leads to high numerical complexity filters even for short delay spread channels. High complexity equalizers implies slow convergence and high numerical load per processed symbol. To save the amount of training or pilot signals and thus increasing the useful data bits, a blind adaptation of the equalizer weights is commonly used. A blind adaptation algorithm in combination with a long equalizer result in even slower convergence. It is therefore desirable to improve the convergence properties of such equalizer schemes. A blind delayless subband equalizer structure is shown to improve the convergence properties of the equalizer. This equalizer consists of a combination of a fullband filtering and and a subband adaptation. In this paper a novel filter bank design and also improved subband-to fullband filter transformation methods is presented. By optimizing the filter bank design, and improving the subband-to-fullband transformation, considerable improvements have been achieved both when it comes to convergence speed and the level of equalization obtained. Simulation results show that the new subband equalization structure has a 12 times faster convergence than its fullband counterpart. The bit error rate is almost the same in both schemes. Thus, there are only advantages by using the suggested equalizer implementation compared to a conventional fullband implementation. The convergence improvement combined with computational savings make it a very attractive technique to use.
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| 9. |
- Nordberg, Jörgen
(author)
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Blind Subband Channel Equalisation
- 2004
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Conference paper (peer-reviewed)abstract
- The wireless communication channel are characterized by its multipath richness. To reverse the effects of even a moderate delay spread, in the linear equalization case, will require an estimation of high order filters.
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| 10. |
- Nordberg, Jörgen, et al.
(author)
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Fractionally Spaced Spatial Adaptive Equalization of S-UMTS Mobile Terminals
- 2002
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In: International journal of adaptive control and signal processing (Print). - : Wiley. - 0890-6327 .- 1099-1115. ; 16:8, s. 541-555
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Journal article (peer-reviewed)abstract
- In this paper we present fractionally spaced adaptive equalization techniques and space diversity combined receiver and evaluate their performance for the downlink of S-UMTS system. The conventional "training" (or non-blind) and the "unsupervised" (or blind)adaptive equalization algorithms are both investigated. Simulation results show that the equalizers are robust to Doppler shift and nonlinearity effects due to TWT amplifiers aboard the satellite. It is also shown that even with a moderate array size of two antenna elements, a significant improvement in terminal performance is achieved.
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