| 1. |
- Dahlberg, Anders, et al.
(författare)
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Multi AP concepts for SCO traffic in a Bluetooth based Radio Infrastructure Network
- 2002
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Konferensbidrag (refereegranskat)abstract
- In this paper, we consider a radio infrastructure network (RIN), which consists of Bluetooth Access Points (APs) to provide services to ad hoc users. The RIN inherently supports both voice and data connectivity. Since Bluetooth offers the establishment of Synchronous Circuit-Oriented (SCO) traffic, the concept under study features a low-cost alternative to indoor cellular base stations. However, a single AP can serve a maximum of only three SCO channels and may not be capable of satisfying the voice traffic demands in hot spots. In order to offer more bandwidth in a location with high voice traffic, two or more APs may be placed in the same coverage area. Respective AP clusters will be denoted as Multi APs. Three Multi AP concepts for doing the SCO allocation are presented and discussed. Our findings show that employing Multi APs significantly reduces the blocking probability.
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| 2. |
- Dahlberg, Anders, et al.
(författare)
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Multi AP Strategies for SCO Traffic in a Bluetooth based Wireless LAN
- 2003
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Konferensbidrag (refereegranskat)abstract
- We consider a Wireless Local Area Network (WLAN) consisting of Bluetooth Access Points (APs). Thus, it inherently offers both ad-hoc voice and data connectivity. As Bluetooth supports Synchronous Circuit-Oriented (SCO) traffic, the concept under study features a low-cost alternative to indoor cellular base stations. Due to the limitation of only three available SCO channels per AP, several APs can be placed in the same coverage area to satisfy voice traffic demands in hot spots. Such AP clusters will be denoted as Multi AP. Three Multi AP strategies for handling the SCO allocation are presented and discussed in terms of signaling and mean time to connect. Our findings show that employing Multi APs significantly reduces the blocking probability. A simple dimensioning rule for the number of APs is given.
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| 3. |
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| 4. |
- Dam, Hai Huyen, et al.
(författare)
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Complex Spreading Sequence Design
- 2002
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Konferensbidrag (refereegranskat)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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| 5. |
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| 6. |
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| 7. |
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| 8. |
- Holland, Ian, et al.
(författare)
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Performance of an Adaptive QAM Scheme over Correlated Rayleigh Fading with Non-zero Delay
- 2004
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Konferensbidrag (refereegranskat)abstract
- Link adaptation techniques have recently been proposed as a spectrally efficient method of obtaining high quality service for mobile communication systems. These schemes aim to better utilise channel capacity compared to fixed transmission schemes, by adapting signal transmission parameters, such as modulation constellation and transmit power. Adaptive modulation schemes, which adapt the modulation constellation, have gained considerable favour for exploiting time-varying channel conditions without increasing the level of co-channel interference. However, the traditional adaptive modulation schemes are designed assuming zero delay between the channel estimation and the modulation mode adaptation. In the case of non-zero delay, the transmitter would update the modulation mode based on outdated channel state information from the receiver. In this paper, we investigate an adaptive quadrature amplitude modulation (AQAM) scheme, which by way of retransmissions, allows a targeted reliability level to be met even in the presence of non-zero delay. The effect of non-zero delay on performance is then investigated. Closed form expressions for the average number of bits per symbol (BPS) throughput and the average bit error rate (BER) of the proposed scheme are derived.
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| 9. |
- Rohani, Behrooz, et al.
(författare)
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Feedback Method for Real-time Perceptual Quality Estimation
- 2004
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Ingår i: Electronics Letters. - : IEE. - 0013-5194 .- 1350-911X. ; 40:14, s. 913-914
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a feedback scheme for real-time estimation of perceptual speech quality is proposed. The feedback information indicates the quality of each previously received speech frame as “good” or “bad”. This information is used in conjunction with the PESQ algorithm to estimate the received speech quality accurately.
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| 10. |
- Shaheem, Asri, et al.
(författare)
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Channel Reliability Metrics for Flat Rayleigh Fading Channels Without Channel State Information
- 2004
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Konferensbidrag (refereegranskat)abstract
- In this paper, iterative decoding of block turbo codes (BTCs) over flat Rayleigh fading channels is considered. The signal is modulated using binary phase shift keying (BPSK) and coherently detected. An exact channel reliability metric that should be passed to the iterative decoder to achieve optimum performance, when no channel state information (CSI) is available at the receiver, is developed. A low complexity cubic approximation to the exact metric, which has no performance loss, is presented. The numerical results obtained using (10,9)^2 single parity check (SPC) BTC, show that the conventional approach, which uses a linear approximation to the channel reliability metric, results in a 27dB penalty at BER of 10^-5 compared to the case where perfect CSI is available. On the other hand, the use of the proposed reliability metric outperforms the existing metric and results in only a 1.1dB performance loss at BER of 10^-5 compared to the use of the metric when the CSI is perfectly known.
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